Metals and Non-metals PYQs – Chemistry, SSC & Railway

Correct Answer: Option 2 — Mg
The reactivity series (activity series) arranges metals in decreasing order of their tendency to lose electrons and form positive ions. The standard order is:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au
All four metals given here appear near the top of this series, but their order among themselves is K > Na > Ca > Mg. Hence magnesium (Mg) stands lowest and is the least reactive of the four.
The difference shows up clearly in their reaction with water. Potassium and sodium react violently with cold water (potassium catches fire), calcium reacts with cold water more gently, while magnesium does not react with cold water at all — it reacts only with hot water, and burns in steam:
⚗️ The Reaction
Mg + 2H₂O (hot) → Mg(OH)₂ + H₂↑
2K + 2H₂O → 2KOH + H₂↑ + heat (catches fire)
• The more reactive the metal, the more vigorously it displaces hydrogen from water.
• Na and K are stored under kerosene because they react even with the moisture of air.
❌ Why the other options are incorrect
✗ Ca — calcium is above Mg in the series; it reacts with cold water to give Ca(OH)₂ and H₂, so it is more reactive than Mg.
✗ K — potassium is the most reactive metal in this set; it reacts with cold water so violently that the hydrogen evolved catches fire.
✗ Na — sodium also reacts vigorously with cold water and is kept under kerosene; it is far more reactive than magnesium.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Au (gold) and Pt are the least reactive metals; they are found in the free (native) state.
• Na and K are stored in kerosene; white phosphorus is stored in water.
• Metals above hydrogen displace H₂ from dilute acids; Cu, Ag and Au do not.
• Mg ribbon burns in air with a dazzling white light giving MgO, a white powder — a classic combination reaction.

Correct Answer: Option 2 — Heating
Rusting is the corrosion of iron. It happens only when iron is exposed to both oxygen (air) and moisture (water) together, and the reddish-brown flaky rust formed is hydrated iron(III) oxide, Fe₂O₃·xH₂O. Rust is porous, so it keeps flaking off and lets fresh iron below get attacked — which is why an iron object can rust right through.
Every genuine method of rust prevention works by cutting off the contact between iron and air/moisture, or by supplying a metal that corrodes in place of iron. Painting, greasing, galvanising, chrome plating, tin plating, anodising and alloying (stainless steel) all do this.
Heating does none of these. In fact heating speeds up a chemical reaction, and heating iron in moist air makes it corrode faster, so heating is not a method of preventing rust.
⚗️ The Reaction
4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O (rust)
• Both air and water must be present — iron does not rust in dry air or in air-free (boiled) water.
• Galvanising coats iron with a layer of zinc; zinc is more reactive, so it corrodes first and saves the iron (sacrificial protection).
❌ Why the other options are incorrect
✗ Painting — a coat of paint forms a physical barrier that keeps oxygen and moisture away from the iron surface; a standard, correct method.
✗ Galvanising — the zinc coating protects iron even if it is scratched, because zinc is above iron in the reactivity series.
✗ Chrome plating — a thin layer of chromium is deposited electrically; it is shiny, hard and does not corrode, so it shields the iron.
📌 SSC & Railway Exam Facts
• Rust = Fe₂O₃·xH₂O (hydrated ferric oxide), reddish-brown and porous.
• Rusting needs oxygen + moisture; it is an oxidation (corrosion) process.
• Galvanisation = coating iron with zinc; tinning = coating with tin (used on food cans).
• Stainless steel = iron + chromium + nickel — an alloy that does not rust.
• Corrosion of copper gives a green coating (basic copper carbonate); silver tarnishes black (Ag₂S).

Correct Answer: Option 1 — Ionic compounds in solid state conduct electricity.
An ionic (electrovalent) compound is formed by the complete transfer of electrons from a metal to a non-metal, giving oppositely charged ions that are held together by a strong electrostatic force in a rigid crystal lattice — for example NaCl, MgCl₂, CaO.
For a substance to conduct electricity it must contain free, movable charge carriers. In the solid state the ions of an ionic compound are locked in fixed positions in the lattice and cannot move, so a solid ionic compound is a non-conductor. The statement in option 1 is therefore false, and since the question asks for the incorrect statement, it is the answer.
When the compound is melted (molten) or dissolved in water, the lattice breaks and the ions become free to move, so it now conducts electricity — such substances are called electrolytes.
⚗️ The Reaction
Na (2, 8, 1) + Cl (2, 8, 7) → Na⁺ (2, 8) + Cl⁻ (2, 8, 8) → NaCl
• The strong electrostatic attraction between Na⁺ and Cl⁻ needs a lot of energy to break, which is why the melting and boiling points are high.
• Molten or aqueous NaCl conducts; solid NaCl does not.
❌ Why the other options are incorrect
✗ Ionic compounds are generally soluble in water — true; water is a polar solvent and pulls the ions apart, so ionic compounds dissolve in water but are insoluble in kerosene and petrol.
✗ Ionic compounds are solids — true; they are hard, brittle crystalline solids because of the strong forces in the lattice.
✗ Ionic compounds have a high melting point — true; a large amount of heat is needed to overcome the strong interionic attraction (NaCl melts at 1074 K).
📌 SSC & Railway Exam Facts
• Ionic compounds conduct in molten and aqueous state only, never in the solid state.
• They are soluble in water, insoluble in organic solvents like kerosene and petrol.
• They are hard and brittle with high melting and boiling points; NaCl m.p. = 1074 K.
• Metal + non-metal → ionic bond; non-metal + non-metal → covalent bond.
• Covalent compounds have low melting points and are poor conductors of electricity.

Correct Answer: Option 1 — Bronze
An alloy is a homogeneous mixture of two or more metals, or of a metal with a non-metal. Alloys are made because they are harder, stronger and more corrosion-resistant than the pure metals they come from.
Bronze is the alloy of copper (Cu) and tin (Sn), roughly 90 % copper and 10 % tin. It is much harder than pure copper, does not corrode easily, and has been used since the Bronze Age for statues, medals, bells and coins.
The classic exam pairing to remember is: brass = copper + zinc, while bronze = copper + tin. Mixing these two up is the commonest mistake in this question.
❌ Why the other options are incorrect
✗ Solder — an alloy of lead (Pb) and tin (Sn); it has a very low melting point, which is why it is used for welding electrical wires. It contains no copper.
✗ Brass — an alloy of copper (Cu) and zinc (Zn), not copper and tin; it is yellow, malleable and used for utensils and musical instruments.
✗ Gold — gold (Au) is a pure element, not an alloy at all. Jewellery gold is an alloy of gold with copper or silver, but gold itself is an element.
📌 SSC & Railway Exam Facts
• Bronze = Cu + Sn; Brass = Cu + Zn; Solder = Pb + Sn; German silver = Cu + Zn + Ni.
• Stainless steel = Fe + Cr + Ni; Steel = Fe + C; Duralumin = Al + Cu + Mg + Mn.
• Amalgam is an alloy in which one metal is mercury (Hg).
• 24 carat gold is pure gold; 22 carat gold contains about 91.6 % gold with copper or silver.
• Alloying changes the properties of a metal — iron rusts, but stainless steel does not.

Correct Answer: Option 4 — pure gold
The carat (also written *karat*) is the unit used to express the purity of gold. The whole scale runs to 24, so 24-carat gold means 24 parts of gold out of 24 parts of metal — that is 100% (about 99.9%) pure gold.
The purity is worked out as percentage of gold = (carat ÷ 24) × 100. Hence 22-carat gold = (22/24) × 100 = 91.6% gold, which is why hallmarked jewellery carries the stamp 916.
Pure 24-carat gold is extremely soft, malleable and ductile, so ornaments cannot be made from it — it would bend out of shape. To harden it, gold is alloyed with copper or silver, and this alloying is exactly what lowers the carat value. Coins, bars and biscuits are made of 24-carat gold; jewellery is usually 22-, 18- or 14-carat.
❌ Why the other options are incorrect
✗ wrought gold — "wrought" describes a metal that has been hammered or worked into shape; the purest commercial form of iron is called wrought iron, not gold.
✗ impure gold — impure gold is gold mixed with other metals, which is precisely less than 24 carat (22, 18, 14 carat, etc.).
✗ spongy gold — "spongy" is the term used for the porous mass of iron obtained in a blast furnace (spongy iron), not a description of pure gold.
📌 SSC & Railway Exam Facts
• 24 carat = 99.9% pure; 22 carat = 91.6% (916 gold); 18 carat = 75%; 14 carat ≈ 58.5%.
• Gold's symbol Au comes from the Latin aurum; its atomic number is 79.
• Gold is the most malleable and most ductile metal — 1 g can be drawn into a wire about 2 km long.
• Gold dissolves only in aqua regia (3 parts conc. HCl : 1 part conc. HNO₃).
• Purity in India is certified by the BIS hallmark; the gold–copper alloy is often called coloured or standard gold.

Correct Answer: Option 4 — Sodium
How a metal behaves with water is a direct reading of its place in the reactivity series. Only the most reactive metals — potassium, sodium and calcium — react with cold water; the middle metals need hot water or steam, and the least reactive ones do not react at all.
Sodium reacts with cold water violently and exothermically, giving sodium hydroxide and hydrogen gas. So much heat is released that the hydrogen catches fire immediately, and the small piece of sodium darts about on the surface. Because of this, sodium and potassium are always stored under kerosene.
⚗️ The Reaction
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + heat
• The solution formed is alkaline, so it turns red litmus blue and phenolphthalein pink.
• The heat evolved ignites the hydrogen, which is why the reaction looks explosive.
• Calcium also reacts with cold water but far more gently: Ca + 2H₂O → Ca(OH)₂ + H₂, and the calcium floats on the bubbles.
❌ Why the other options are incorrect
✗ Iron — does not react with cold or hot water; it reacts only with steam: 3Fe + 4H₂O → (steam) Fe₃O₄ + 4H₂.
✗ Aluminium — a tough, thin layer of aluminium oxide (Al₂O₃) protects it, so it does not attack cold water; it reacts only with steam: 2Al + 3H₂O → Al₂O₃ + 3H₂.
✗ Zinc — lies below aluminium in reactivity and reacts only with steam: Zn + H₂O → ZnO + H₂.
📌 SSC & Railway Exam Facts
• Cold water — K, Na, Ca; hot water — Mg; steam — Al, Zn, Fe; no reaction — Pb, Cu, Ag, Au.
• Potassium reacts most violently of all; sodium and potassium are kept in kerosene to stop them reacting with air and moisture.
• Metal + water → metal hydroxide (or oxide) + hydrogen.
• Magnesium in hot water floats because bubbles of H₂ stick to its surface.
• Sodium's symbol Na comes from natrium; NaOH is caustic soda.

Correct Answer: Option 4 — Only A
Check each statement against the reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
A is correct. Both zinc and lead stand above copper in the series, so both are more reactive than copper. This is why zinc and lead can displace copper from copper sulphate solution, while copper cannot displace either of them.
B is incorrect — it is simply the opposite of A, and A and B can never both be true.
C is incorrect. When an iron nail is dipped in blue copper sulphate solution, iron (being above copper) displaces the copper, which deposits on the nail as a reddish-brown / brownish layer — not yellow. At the same time the solution changes from blue to pale green because iron(II) sulphate is formed.
Only statement A survives, so the answer is Only A.
⚗️ The Reaction
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
• The nail gets a reddish-brown coating of copper, never a yellow one.
• The solution turns from blue (CuSO₄) to pale green (FeSO₄).
• This is a displacement reaction and also a redox reaction: Fe is oxidised, Cu²⁺ is reduced.
❌ Why the other options are incorrect
✗ Only C — C is false; the nail turns brownish, not yellow, and A is true, so C alone cannot be the answer.
✗ Only A and B — A and B are directly contradictory statements; both can never be correct together.
✗ Only A and C — A is correct but C is wrong because of the yellow colour claim.
📌 SSC & Railway Exam Facts
• CuSO₄·5H₂O = blue vitriol (blue); FeSO₄·7H₂O = green vitriol (pale green); ZnSO₄·7H₂O = white vitriol.
• A metal displaces from solution only a metal placed below it in the reactivity series.
• Zn + CuSO₄ → ZnSO₄ + Cu and Pb + CuSO₄ → PbSO₄ + Cu both take place.
• Cu + FeSO₄ → no reaction, because copper is less reactive than iron.
• Most reactive metal in the series is potassium (K); least reactive is gold (Au).

Correct Answer: Option 4 — Electrolytic refining
The metal obtained after reduction of its ore is still impure, so the last step of metallurgy is refining. The most widely used and most reliable method is electrolytic refining, used for copper, zinc, tin, nickel, silver, gold and aluminium.
The arrangement is easy to remember:
• Anode (+) — a thick block of the impure metal.
• Cathode (−) — a thin strip of the pure metal.
• Electrolyte — a solution of a salt of the same metal, e.g. acidified CuSO₄ for copper.
When current is passed, the impure anode dissolves into the solution as metal ions, and an equivalent amount of pure metal is deposited on the cathode. The soluble impurities go into the solution, while the insoluble impurities — often valuable metals such as silver, gold and platinum — fall to the bottom below the anode. This deposit is called anode mud (anode sludge).
❌ Why the other options are incorrect
✗ Painting — this only puts a protective coat on the metal surface to prevent rusting; it does not remove any impurity.
✗ Oiling — greasing or oiling also merely keeps air and moisture away to stop corrosion of tools and machine parts.
✗ Galvanisation — coating iron or steel with a layer of zinc to prevent rusting; again a protection method, not a purification method.
📌 SSC & Railway Exam Facts
• Impure metal = anode; pure metal = cathode; salt solution of the metal = electrolyte.
• The impurities collecting below the anode are the anode mud, from which Ag, Au and Pt are recovered.
• Order of metallurgy: concentration → roasting/calcination → reduction → refining.
• Roasting = heating a sulphide ore in excess air; calcination = heating a carbonate ore in limited air.
• Other refining methods: distillation (Zn, Hg), liquation (Sn, Pb), poling (Cu), zone refining (Si, Ge).

Correct Answer: Option 2 — Bromine
Bromine (Br) is the only non-metal that is liquid at room temperature. It is a reddish-brown, dense, fuming liquid with a sharp, choking smell; its melting point is −7 °C and its boiling point is 59 °C, so at 25 °C it is comfortably a liquid. It belongs to Group 17, the halogens, and exists as the diatomic molecule Br₂.
Most non-metals are gases (H₂, O₂, N₂, Cl₂) or brittle solids (carbon, sulphur, phosphorus, iodine) at room temperature. Bromine is the single liquid exception, which is exactly why it is asked so often.
❌ Why the other options are incorrect
✗ Oxygen — a colourless gas at room temperature (O₂); it liquefies only below −183 °C.
✗ Fluorine — a pale-yellow gas and the most reactive non-metal of all; its boiling point is about −188 °C.
✗ Mercury — this is indeed a liquid at room temperature, but it is a metal, not a non-metal, so it does not answer the question. It is the only liquid metal.
📌 SSC & Railway Exam Facts
• Bromine = the only liquid non-metal; Mercury = the only liquid metal.
• Gallium (30 °C) and Caesium (28 °C) are metals that melt in the palm of the hand.
• Iodine is a lustrous solid non-metal that sublimes to a violet vapour.
• Graphite (an allotrope of carbon) is the non-metal that conducts electricity; diamond is the hardest natural substance.
• Halogens (Group 17): F and Cl gases, Br liquid, I and At solids.

Correct Answer: Option 1 — CuSO₄
In the electrolytic refining of copper, the electrolyte must contain the same metal ion that is being refined, so that copper can dissolve at one electrode and deposit at the other. The electrolyte used is an acidified aqueous solution of copper sulphate (CuSO₄ + a little dilute H₂SO₄).
The thick block of impure copper is made the anode and a thin strip of pure copper the cathode. On passing current, copper of the anode dissolves as Cu²⁺ ions and an equal amount of pure copper is deposited on the cathode. The soluble impurities go into solution, while the insoluble ones — gold, silver and platinum — fall below the anode as anode mud, a valuable by-product.
⚗️ At the Electrodes
Anode: Cu(s) → Cu²⁺(aq) + 2e⁻ | Cathode: Cu²⁺(aq) + 2e⁻ → Cu(s)
• The anode gets thinner and the cathode gets thicker.
• The concentration of CuSO₄ stays constant, because as much Cu²⁺ enters the solution as leaves it.
❌ Why the other options are incorrect
✗ CuO — copper(II) oxide is an insoluble solid and cannot serve as an electrolyte solution; it is a reduction raw material in smelting, not in refining.
✗ Na₂SO₄ — it would supply Na⁺ ions, so hydrogen would be released at the cathode instead of copper being deposited.
✗ Cu₂Cl₂ — copper(I) chloride is almost insoluble in water and unstable, so it cannot maintain a steady supply of Cu²⁺ ions.
📌 SSC & Railway Exam Facts
• Impure metal = anode, pure metal = cathode, salt of the same metal = electrolyte.
• Anode mud of copper refining is a source of gold, silver, platinum and selenium.
• CuSO₄·5H₂O = blue vitriol (nila thotha); on heating it turns white, losing water of crystallisation.
• Roasting (sulphide ore + O₂) and calcination (carbonate ore, limited air) both precede reduction to the metal.
• Copper's chief ore is copper pyrites, CuFeS₂.

Correct Answer: Option 1 — Hydrogen gas
Normally a metal reacting with an acid gives hydrogen, but nitric acid (HNO₃) is a strong oxidising agent: it oxidises the hydrogen produced into water, and is itself reduced to oxides of nitrogen (N₂O, NO, NO₂). That is why HNO₃ generally does not give hydrogen gas with metals.
Magnesium (Mg) and manganese (Mn) are the two standard exceptions. With very dilute nitric acid these two metals are so reactive, and the acid so weakly oxidising at that dilution, that the hydrogen escapes as H₂ gas before it can be oxidised.
⚗️ The Reaction
Mg + 2HNO₃(very dilute) → Mg(NO₃)₂ + H₂↑
Mn + 2HNO₃(very dilute) → Mn(NO₃)₂ + H₂↑
• Both metals lie above hydrogen in the reactivity series, so they displace it from the acid.
• Atom count in the first equation: 1 Mg, 2 H, 2 N, 6 O on each side — balanced.
• The gas burns with a pop sound when a burning splint is brought near it — the test for H₂.
❌ Why the other options are incorrect
✗ Nitrogen gas — N₂ is not liberated here; nitric acid may be reduced to nitrogen oxides, but not to free nitrogen in this reaction.
✗ Helium gas — He is an inert noble gas; it takes part in no chemical reaction and is not present in either reactant.
✗ Oxygen gas — O₂ is not produced by a metal–acid reaction; oxygen from the acid ends up in the salt and in water.
📌 SSC & Railway Exam Facts
• Metal + dilute acid → salt + hydrogen, but HNO₃ is the exception because it is an oxidising acid.
• Only Mg and Mn give H₂ with very dilute HNO₃ — a classic PYQ pair.
• Test for hydrogen: burns with a "pop" sound. Test for CO₂: turns lime water milky.
• Aqua regia = 3 HCl : 1 HNO₃, and it dissolves gold and platinum.
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au; metals below H do not displace hydrogen from acids.

Correct Answer: Option 1 — Copper
Whether a metal reacts with a dilute acid is decided by its position in the reactivity series:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au
Only a metal placed above hydrogen can displace hydrogen from a dilute acid. Copper lies below hydrogen, so it has a lower tendency to lose electrons than hydrogen and cannot displace H⁺ — that is, copper does not react with dilute HCl or dilute H₂SO₄ and gives no hydrogen gas. Of the four metals given, copper is therefore the least reactive with acids.
Copper does dissolve in hot concentrated H₂SO₄ or in HNO₃, but that is an oxidation by the acid, not a hydrogen-displacement reaction.
⚗️ Compare the Reactions
Zn + 2HCl(dilute) → ZnCl₂ + H₂↑ | Fe + 2HCl(dilute) → FeCl₂ + H₂↑
Cu + HCl(dilute) → no reaction
• Metals above H displace hydrogen; metals below H do not.
• The order of reactivity among the options is Al > Zn > Fe > Cu.
❌ Why the other options are incorrect
✗ Aluminium — the most reactive of the four; 2Al + 6HCl → 2AlCl₃ + 3H₂↑. Its apparent resistance in air is due to a protective oxide layer (Al₂O₃), not low reactivity.
✗ Iron — lies above hydrogen and reacts with dilute acids to give H₂; it also rusts readily in moist air.
✗ Zinc — reacts vigorously with dilute HCl and H₂SO₄; it is the standard metal used in the laboratory preparation of hydrogen gas.
📌 SSC & Railway Exam Facts
• Metals below hydrogen (Cu, Hg, Ag, Au, Pt) do not displace H₂ from dilute acids.
• Gold and platinum dissolve only in aqua regia (3 HCl : 1 HNO₃).
• Galvanisation = coating iron with zinc, which protects the iron because zinc is more reactive.
• Copper vessels form a green coating of basic copper carbonate, CuCO₃·Cu(OH)₂, in moist air.
• Most reactive metal — potassium (K/Cs); least reactive — gold (Au) in the school series.

Correct Answer: Option 4 — Black-coloured copper (II) oxide
When copper is heated strongly in air, the oxygen of the air combines with it and the shiny reddish-brown metal becomes coated with a black layer. This black substance is copper(II) oxide, CuO, in which copper shows the +2 oxidation state. The reaction is a combination reaction and also an oxidation.
The colour is the giveaway in this question: CuO is black, while copper(I) oxide, Cu₂O, is red/reddish-brown. So both the colour (black) and the oxidation state (II) in Option 4 are right.
The change can be reversed — passing hydrogen gas over hot CuO turns the black layer back to the brown colour of copper metal, a standard reduction demonstration.
⚗️ The Reaction
2Cu + O₂ → (heat) 2CuO
• Copper is oxidised; the black coating on the surface is CuO.
• Reverse reduction: CuO + H₂ → (heat) Cu + H₂O — black turns back to brown.
• This is why copper vessels turn dull and blackish when heated in air.
❌ Why the other options are incorrect
✗ Brown-coloured copper(II) oxide — the oxidation state is right but the colour is wrong; CuO is black, and brown is the colour of copper metal itself.
✗ Blue-coloured copper(II) oxide — blue is the colour of hydrated copper sulphate, CuSO₄·5H₂O, not of copper oxide.
✗ Black-coloured copper (I) oxide — the colour is right but the oxidation state is wrong; copper(I) oxide, Cu₂O, is red, not black.
📌 SSC & Railway Exam Facts
• CuO = copper(II) oxide = black; Cu₂O = copper(I) oxide = red.
• 2Cu + O₂ → 2CuO is a combination as well as an oxidation reaction.
• Copper exposed to moist air slowly forms a green coating of basic copper carbonate, CuCO₃·Cu(OH)₂ — the corrosion of copper.
• CuSO₄·5H₂O = blue vitriol (blue); on heating it loses water and turns white.
• Copper is a very good conductor of heat and electricity, so it is used in wires and utensils; symbol Cu from Latin cuprum.

Correct Answer: Option 1 — All metals are equally reactive.
This is an INCORRECT-type question, so the false statement is the answer. Metals are not equally reactive at all — their reactivities differ so widely that chemists arrange them in a reactivity series:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au
Potassium and sodium react violently even with cold water, magnesium needs hot water, iron and zinc need steam, while silver and gold do not react with water or even with dilute acids. Clearly, Option 1 is false and is the required answer.
The remaining three statements are all true. Option 3 is simply the correct opposite of Option 1. Silver lies far below sodium, so it is less reactive. Potassium is the most reactive metal of the series and gold the least reactive, which is why gold is found free (native) in nature and does not tarnish.
❌ Why the other options are incorrect
✗ Silver is less reactive than sodium — true; Ag lies near the bottom of the series while Na is near the top.
✗ All metals are not equally reactive — true; this is precisely why the reactivity series exists.
✗ Potassium is more reactive than gold — true; K is the most reactive and Au the least reactive metal listed.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• With water: cold water — K, Na, Ca; hot water — Mg; steam — Al, Zn, Fe; no reaction — Pb, Cu, Ag, Au.
• Metals above hydrogen displace H₂ from dilute acids; those below it do not.
• Gold, silver and platinum are called noble metals because they resist corrosion and occur native.
• Sodium and potassium are stored in kerosene because they react vigorously with air and moisture.

Correct Answer: Option 3 — Na
The method used to extract a metal depends on its position in the reactivity series.
Metals of high reactivity — K, Na, Ca, Mg and Al — hold their ores so strongly that no chemical reducing agent (carbon, CO, aluminium) can reduce them. They are therefore obtained by the electrolytic reduction of their molten (fused) salts or oxides. Sodium is extracted by the electrolysis of molten sodium chloride in the Down's process: Na⁺ ions move to the cathode and are reduced to sodium metal, while Cl⁻ ions are oxidised to chlorine gas at the anode.
Metals of middle reactivity (Zn, Fe, Pb, Cu) are first converted to their oxides by roasting/calcination and then reduced with carbon. Metals of low reactivity (Ag, Au, Pt) occur free or need only mild heating.
⚗️ The Reaction
2NaCl(l) → (electrolysis) 2Na(s) + Cl₂(g)
• At the cathode (reduction): Na⁺ + e⁻ → Na.
• At the anode (oxidation): 2Cl⁻ → Cl₂ + 2e⁻.
• Aluminium is obtained the same way from molten Al₂O₃ in cryolite — the Hall–Héroult process.
❌ Why the other options are incorrect
✗ Zn — a moderately reactive metal; zinc oxide is reduced by carbon: ZnO + C → Zn + CO.
✗ Pb — also moderately reactive; PbO + C → Pb + CO, so carbon reduction is enough.
✗ Ag — a least reactive metal found largely in the free state; its ores are reduced very easily and it is refined, not extracted, electrolytically.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Top of the series → electrolytic reduction; middle → carbon reduction; bottom → found free.
• Down's process → Na; Hall–Héroult process → Al.
• Roasting = heating a sulphide ore in excess air; calcination = heating a carbonate ore in limited air.
• In electrolytic refining, the impure metal is the anode, the pure metal the cathode, and the impurities settle as anode mud.

Correct Answer: Option 4 — oxides, sulphides and carbonates
The minerals from which a metal can be extracted profitably and conveniently are called its ores. Except for the least reactive metals (gold, silver, platinum), which occur in the free or native state, all metals are found in the crust in the combined state — chemically joined to oxygen, sulphur, carbonate, halide or sulphate groups.
So the ores of the Earth's crust are of many kinds together, the three commonest classes being:
• Oxides — bauxite (Al₂O₃·2H₂O), haematite (Fe₂O₃), zincite (ZnO)
• Sulphides — zinc blende (ZnS), cinnabar (HgS), copper glance (Cu₂S), galena (PbS)
• Carbonates — calamine (ZnCO₃), siderite (FeCO₃), limestone (CaCO₃), malachite
Because oxides are the easiest to reduce, sulphide ores are first roasted and carbonate ores calcined — both converting the ore into its oxide before reduction.
❌ Why the other options are incorrect
✗ only carbonates — carbonates are just one class of ore; haematite (oxide) and galena (sulphide) are equally important and disprove the word "only".
✗ only oxides — oxides are the commonest class, but zinc blende (ZnS) and calamine (ZnCO₃) show that other classes exist.
✗ only sulphides — sulphides are typical of the middle of the reactivity series; the ores of aluminium and iron are oxides, not sulphides.
📌 SSC & Railway Exam Facts
• Roasting — sulphide ore heated in excess air: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
• Calcination — carbonate ore heated in limited air: ZnCO₃ → ZnO + CO₂.
• Aluminium — bauxite; Iron — haematite/magnetite; Zinc — zinc blende/calamine; Mercury — cinnabar; Lead — galena.
• Aluminium is the most abundant metal and oxygen the most abundant element in the Earth's crust.
• Gravity separation, froth flotation, magnetic separation and leaching are methods of concentrating an ore.

Correct Answer: Option 4 — Gold and silver
Whether a metal occurs free (native) or combined in the Earth's crust is decided entirely by its chemical reactivity.
Metals at the bottom of the reactivity series — copper, mercury, silver, gold and platinum — are very unreactive. They do not react readily with the oxygen, moisture, carbon dioxide or acids of the environment, so they survive in the crust as the metal itself. Gold and silver are the standard textbook examples of metals found in the free or native state; gold is so unreactive that ancient ornaments are still bright today.
Metals at the top of the series — potassium, sodium, calcium, magnesium and aluminium — are so reactive that they combine at once with air and water. Sodium and potassium even catch fire in air and react violently with cold water, which is why sodium is stored under kerosene and is never found free in nature.
❌ Why the other options are incorrect
✗ Sodium and potassium — both are extremely reactive; they react violently with cold water and are always found as compounds such as NaCl and KCl.
✗ Silver and potassium — silver is indeed found free, but potassium is one of the most reactive metals and never occurs in the native state.
✗ Gold and sodium — gold is found free, but sodium is highly reactive and occurs only in the combined state.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Metals found native: gold (Au), silver (Ag), platinum (Pt), and sometimes copper.
• Sodium and potassium are stored under kerosene because they react vigorously with air and water.
• Gold is the most ductile and most malleable metal; its purity is measured in carats — 24 carat = pure gold.
• Silver is the best conductor of heat and electricity among all metals.

Correct Answer: Option 1 — Gold
Ductility is the property of a metal by which it can be drawn into thin wires. Gold (Au) is the most ductile metal known — a single gram of gold can be drawn into a wire about 2 km long. Gold is also the most malleable metal, meaning it can be beaten into the thinnest sheets (gold leaf, only a few hundred atoms thick).
The reason is the metallic bond. In a metal the layers of positive ions are held together by a sea of free electrons; when a stress is applied the layers can slide over one another without the bond breaking, because the mobile electrons simply re-adjust. In gold these layers slide very easily, so it neither cracks nor snaps.
Because of this, gold is used in jewellery, in fine electronic contacts and in spacecraft coatings. Silver is the second most ductile metal.
❌ Why the other options are incorrect
✗ Lead — lead is malleable but very poorly ductile; it has low tensile strength and the wire breaks on drawing, which is why lead wires are not made.
✗ Sodium — an alkali metal so soft that it can be cut with a knife; it is not drawn into wires, and it is so reactive that it is stored under kerosene.
✗ Lithium — the lightest metal (density 0.53 g/cm³), also soft and highly reactive; it is used in batteries, not for wire-drawing.
📌 SSC & Railway Exam Facts
• Gold is the most ductile and most malleable metal; silver comes second.
• Ductility = drawn into wires; Malleability = beaten into sheets.
• Best conductor of electricity: silver > copper > gold > aluminium.
• Hardest metal = tungsten (W); softest metals = caesium and sodium (cut with a knife).
• Lithium is the lightest metal; mercury is the only metal that is liquid at room temperature; osmium is the densest.

Correct Answer: Option 2 — Metal salt
Electrolytic refining is the final step of metallurgy, used to obtain a metal in a very pure form. The arrangement is always the same:
• Anode (+) — a thick block of the impure metal.
• Cathode (−) — a thin strip of the pure metal.
• Electrolyte — a solution of a salt of the same metal, i.e. a metal salt solution.
When current is passed, the impure metal at the anode dissolves into the electrolyte as metal ions, and an equivalent amount of pure metal is deposited on the cathode. The soluble impurities stay in solution while the insoluble ones fall below the anode as anode mud, from which valuable metals like gold, silver, platinum and selenium are recovered.
For the refining of copper, the electrolyte used is acidified copper sulphate solution (CuSO₄ + dilute H₂SO₄) — a metal salt.
❌ Why the other options are incorrect
✗ Impure metal — the impure metal is the anode, a solid electrode; it is not the electrolyte.
✗ Combination of pure metal and metal salt — the pure metal is the cathode, again a solid electrode; only the salt solution serves as the electrolyte.
✗ Pure metal — this is the cathode on which the refined metal is deposited, not the conducting medium between the electrodes.
📌 SSC & Railway Exam Facts
• Metallurgy steps: concentration → roasting/calcination → reduction → refining.
• Roasting — heating a sulphide ore in excess air; Calcination — heating a carbonate ore in limited air.
• In electrolysis, oxidation occurs at the anode and reduction at the cathode.
• Anode mud is the valuable source of Au, Ag, Pt and Se.
• Highly reactive metals such as Na, K, Ca, Mg and Al are obtained by the electrolytic reduction of their molten chlorides or oxides.

Correct Answer: Option 4 — 1, 2 and 3
All three statements describe standard physical properties of metals, so every one of them is correct.
Statement 1 — Malleability. Metals can be hammered or beaten into thin sheets without breaking. Gold and silver are the most malleable metals; aluminium foil is used to wrap food and iron sheets are rolled for car bodies.
Statement 2 — Ductility. Metals can be drawn into thin wires. Gold is the most ductile metal — about 2 km of wire can be drawn from 1 g of gold; copper and aluminium wires carry our electricity.
Statement 3 — Thermal conductivity. Metals possess free (delocalised) electrons, which carry heat rapidly through the lattice. Silver is the best conductor of heat, followed by copper, which is why cooking utensils are made of copper and aluminium. Metals are also lustrous, sonorous, hard, and have high melting points and densities.
❌ Why the other options are incorrect
✗ Only 1 — it ignores statements 2 and 3; ductility and thermal conductivity are equally standard metallic properties.
✗ Only 1 and 3 — statement 2 is also correct; drawing a metal into wire is exactly what ductility means.
✗ Only 1 and 2 — statement 3 is correct as well; the free electrons of a metal make it a good conductor of both heat and electricity.
📌 SSC & Railway Exam Facts
• Most malleable and most ductile metal — gold (Au); silver is next.
• Best conductors of heat and electricity: silver > copper > gold > aluminium.
• Poorest metallic conductors — lead and mercury; mercury is the only liquid metal.
• Sonorous metals ring when struck — that is why school bells are made of metal.
• Exceptions to remember: sodium and potassium are soft (cut with a knife), gallium and caesium melt in the palm, and graphite (a non-metal) conducts electricity.

Correct Answer: Option 1 — Silver
The reactivity series (activity series) arranges metals in the decreasing order of their chemical reactivity, that is, in the order of how readily they lose electrons and form positive ions:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au
Copper (Cu) lies below hydrogen and is therefore a fairly unreactive metal, but it still stands above mercury, silver and gold. Of the four options, only silver (Ag) lies below copper, so copper is more reactive than silver. Calcium, sodium and potassium all lie far above copper and are much more reactive than it.
This order is verified experimentally: copper displaces silver from silver nitrate solution, the blue Cu²⁺ colour appearing while shining silver is deposited on the copper wire.
⚗️ The Reaction
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
• Copper displaces silver because it is higher in the reactivity series — proof that Cu is more reactive than Ag.
• The colourless solution turns blue due to Cu(NO₃)₂, and greyish-white silver settles on the copper.
• The reverse reaction — silver displacing copper — never happens, since Ag is below Cu.
❌ Why the other options are incorrect
✗ Calcium — Ca stands far above Cu in the series; it even reacts with cold water to give Ca(OH)₂ + H₂, which copper never does.
✗ Sodium — Na is among the most reactive metals; it reacts violently with cold water and is stored under kerosene.
✗ Potassium — K is the most reactive metal of the series; its reaction with water is so vigorous that the hydrogen catches fire.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Metals below hydrogen (Cu, Hg, Ag, Au) do not liberate H₂ from dilute acids.
• Gold and platinum are the least reactive and occur in the native (free) state.
• Na and K are stored in kerosene; phosphorus is stored in water.
• Fe + CuSO₄ → FeSO₄ + Cu — iron displaces copper, so iron vessels cannot store copper sulphate solution.

Correct Answer: Option 2 — Both Zn and CO
This is the reduction step of zinc extraction. After roasting zinc sulphide ore (or calcining zinc carbonate ore) the metal is obtained as zinc oxide, ZnO. This oxide is then reduced to the metal by heating it with carbon (coke), which acts as the reducing agent.
Carbon has a greater affinity for oxygen than zinc has, so it takes the oxygen away from ZnO. The zinc is thereby reduced to free metal, while the carbon is oxidised to carbon monoxide (CO). Because both oxidation and reduction happen together, this is a redox reaction, and it is also a displacement reaction — carbon displaces zinc from its oxide.
Carbon reduction works only for the oxides of moderately reactive metals such as Zn, Fe, Pb and Cu. The highly reactive metals — K, Na, Ca, Mg and Al — cannot be reduced by carbon and must be obtained by the electrolysis of their molten salts.
⚗️ The Reaction
ZnO(s) + C(s) → (heat) Zn(s) + CO(g)
• ZnO is reduced (loses oxygen) to Zn; carbon is oxidised (gains oxygen) to CO.
• Count the atoms: 1 Zn, 1 C and 1 O on each side — the equation is balanced as written.
• With an excess of oxide the carbon can be taken all the way to CO₂, but the standard NCERT equation for zinc gives CO.
❌ Why the other options are incorrect
✗ Only Zn — the carbon cannot simply vanish; the oxygen it removes must leave as a carbon oxide, so a gaseous product is compulsory.
✗ Only CO — the whole purpose of the step is to obtain the metal; zinc must appear among the products.
✗ Zn and CO₂ — the standard equation for the reduction of ZnO by carbon gives CO, not CO₂; CO₂ would require ZnO + C in a 2 : 1 ratio (2ZnO + C → 2Zn + CO₂).
📌 SSC & Railway Exam Facts
• Roasting — heating a sulphide ore in excess air; calcination — heating a carbonate ore in limited air.
• 2ZnS + 3O₂ → 2ZnO + 2SO₂ (roasting); ZnCO₃ → (heat) ZnO + CO₂ (calcination).
• Carbon reduction works for Zn, Fe, Pb, Cu; K, Na, Ca, Mg, Al need electrolytic reduction.
• In the thermite reaction, Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat, used for welding railway tracks.
• Zinc's chief ores: zinc blende (ZnS), calamine (ZnCO₃) and zincite (ZnO).

Correct Answer: Option 3 — Mn
Nitric acid (HNO₃) is a strong oxidising agent. When a metal reacts with it, the hydrogen that is set free is immediately oxidised by the acid itself to water, and the nitric acid is reduced to an oxide of nitrogen (N₂O, NO or NO₂). That is why HNO₃ normally does not give hydrogen gas with metals — the standard exception among all the common acids.
There are just two exceptions to memorise, and NCERT states them plainly: magnesium (Mg) and manganese (Mn) react with very dilute nitric acid to evolve hydrogen gas. Of the four options, only Mn is one of them.
The acid must be very dilute — in that condition its oxidising power is weak enough for the hydrogen to escape as H₂ before it can be oxidised.
⚗️ The Reaction
Mn(s) + 2HNO₃(aq, very dilute) → Mn(NO₃)₂(aq) + H₂(g)
• Manganese displaces hydrogen from the acid because it lies above hydrogen in the reactivity series.
• Balance check: 1 Mn, 2 H, 2 N and 6 O on each side.
• With concentrated or moderately dilute HNO₃ the same metal would give nitrogen oxides and water instead of H₂.
❌ Why the other options are incorrect
✗ Fe — iron reacts with dilute HCl and dilute H₂SO₄ to give H₂, but with nitric acid the liberated hydrogen is oxidised to water; concentrated HNO₃ even makes iron passive by forming a protective oxide layer.
✗ Zn — zinc gives H₂ readily with dilute HCl/H₂SO₄ (Zn + 2HCl → ZnCl₂ + H₂), but with HNO₃ it yields nitrogen oxides, not hydrogen.
✗ Al — aluminium too gives H₂ with dilute HCl and NaOH, but concentrated HNO₃ renders aluminium passive, forming a tight Al₂O₃ coat that stops further reaction.
📌 SSC & Railway Exam Facts
• Only Mg and Mn liberate H₂ with very dilute HNO₃ — a repeatedly asked NCERT line.
• HNO₃ is an oxidising acid; with other metals it gives N₂O, NO or NO₂, not H₂.
• Metal + dilute acid → salt + hydrogen gas; the gas burns with a pop sound.
• Metals below hydrogen (Cu, Hg, Ag, Au) do not displace hydrogen from dilute acids at all.
• Aqua regia = 3 parts conc. HCl + 1 part conc. HNO₃, the only reagent that dissolves gold and platinum.

Correct Answer: Option 1 — White
When a magnesium ribbon is heated in air it burns with a dazzling white flame, giving a white powdery ash of magnesium oxide (MgO). This is the very first experiment of the NCERT chapter on chemical reactions, and the phrase “burns with a dazzling white flame” is quoted exactly in exams.
The ribbon must be cleaned with sandpaper before burning, because magnesium reacts slowly with moist air and gets covered by a protective layer of magnesium oxide that would otherwise stop it from catching fire.
The reaction is a combination reaction (two substances form one product) and also an oxidation, since magnesium gains oxygen. The white ash MgO is a basic oxide; dissolved in water it gives magnesium hydroxide, Mg(OH)₂, the milk of magnesia used as an antacid. Because the flame is so bright, magnesium is used in fireworks, flares and old photographic flash bulbs.
⚗️ The Reaction
2Mg(s) + O₂(g) → (burning) 2MgO(s)
• Balance check: 2 Mg and 2 O on each side — the coefficient 2 is needed before both Mg and MgO.
• Magnesium gains oxygen, so it is oxidised; the reaction is both a combination and a redox reaction.
• MgO + H₂O → Mg(OH)₂ — the white ash gives a base, which turns red litmus blue.
❌ Why the other options are incorrect
✗ Red — a crimson-red flame is the flame test for strontium (and lithium), not for magnesium.
✗ Pink — a pink/lilac flame is characteristic of potassium salts in the flame test.
✗ Green — a green flame is given by copper (bluish-green) and barium (apple-green) salts.
📌 SSC & Railway Exam Facts
• Magnesium burns with a dazzling white flame to give white MgO: 2Mg + O₂ → 2MgO.
• Flame colours: Na — golden yellow, K — lilac/pink, Ca — brick red, Cu — bluish green, Ba — apple green.
• MgO + H₂O → Mg(OH)₂ (milk of magnesia), used as an antacid and a mild laxative.
• The magnesium ribbon is cleaned with sandpaper to remove the oxide layer before burning.
• Metal + oxygen → basic oxide; non-metal + oxygen → acidic oxide (e.g. SO₂, CO₂).

Correct Answer: Option 3 — Magnesium
A metal's reaction with water follows its position in the reactivity series. Potassium, sodium and calcium are so reactive that they attack cold water, but magnesium does not react with cold water — it reacts only with hot water, and more vigorously with steam.
Magnesium is placed just below calcium in the series. In cold water the reaction is far too slow to be seen; when the metal is put in hot water, however, hydrogen bubbles stick to its surface and make the ribbon float, giving magnesium hydroxide, Mg(OH)₂. With steam it forms magnesium oxide, MgO, and hydrogen.
Remember the ladder for reaction with water: K, Na, Ca → cold water; Mg → hot water; Al, Zn, Fe → steam only; Pb, Cu, Ag, Au → no reaction with water at all.
⚗️ The Reaction
Mg(s) + 2H₂O(l) → (hot water) Mg(OH)₂(aq) + H₂(g)
Mg(s) + H₂O(g) → (steam) MgO(s) + H₂(g)
• With cold water there is no observable reaction; hot water is needed to start it.
• Balance check for the first equation: 1 Mg, 4 H and 2 O on each side.
• The hydrogen bubbles cling to the ribbon and make it float — the classic laboratory observation.
❌ Why the other options are incorrect
✗ Sodium — Na reacts violently with cold water, and the reaction is so exothermic that the hydrogen catches fire: 2Na + 2H₂O → 2NaOH + H₂ + heat.
✗ Calcium — Ca reacts with cold water too, though less violently; the hydrogen bubbles stick to the metal and make it float: Ca + 2H₂O → Ca(OH)₂ + H₂.
✗ Potassium — K is the most reactive of the four and reacts with cold water most vigorously of all, the hydrogen catching fire at once.
📌 SSC & Railway Exam Facts
• Reaction with water: K, Na, Ca → cold water; Mg → hot water; Al, Zn, Fe → steam; Cu, Ag, Au → none.
• Na and K are stored in kerosene because they catch fire on contact with moist air.
• 3Fe + 4H₂O → (steam) Fe₃O₄ + 4H₂ — iron reacts only with steam, never with cold water.
• Metal + water → metal hydroxide (or oxide) + hydrogen; the H₂ burns with a pop sound.
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.

Correct Answer: Option 1 — Sodium
Sodium (Na) is the most reactive metal among the four given and sits very high in the reactivity series. It reacts so vigorously with the oxygen and moisture of air that the heat released is enough to set the metal on fire by itself at ordinary temperature.
For this reason sodium and potassium are always stored under kerosene oil, which keeps air and water away from the metal surface. Phosphorus, a non-metal that catches fire in air in the same way, is stored under water.
⚗️ The Reaction
4Na + O₂ → 2Na₂O
2Na + 2H₂O → 2NaOH + H₂ + heat
• The reaction with water is so exothermic that the hydrogen released catches fire immediately.
• Na₂O + H₂O → 2NaOH, a strong base, which is why sodium's oxide is a basic oxide.
❌ Why the other options are incorrect
✗ Copper — a very unreactive metal placed below hydrogen in the reactivity series; in moist air it only slowly forms a green coating of basic copper carbonate, CuCO₃·Cu(OH)₂.
✗ Zinc — moderately reactive; it forms a protective layer of zinc oxide in air and needs strong heating before it burns.
✗ Magnesium — it burns with a dazzling white light, but only after being heated; it does not ignite on its own merely by being left in the open.
📌 SSC & Railway Exam Facts
• Reactivity series (high to low): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt.
• Sodium and potassium are stored in kerosene; white phosphorus is stored in water.
• Sodium is so soft that it can be cut with a knife, and its density is less than that of water.
• Burning magnesium ribbon gives white magnesium oxide (MgO) ash — a classic combination reaction.
• Gold and platinum are the least reactive metals and occur in the free (native) state.

Correct Answer: Option 1 — Gallium and cesium
Most metals have very high melting points because of the strong metallic bonding between their positive ions and the sea of delocalised electrons. Gallium and caesium are the famous exceptions: their metallic bonding is unusually weak, so they melt just above ordinary room temperature.
• Melting point of gallium (Ga) ≈ 29.8 °C — a piece of gallium melts in the palm of the hand.
• Melting point of caesium (Cs) ≈ 28.4 °C, the lowest of any metal that is solid at 25 °C.
This is why NCERT states that gallium and caesium have such low melting points that they will melt if kept on the palm. Mercury (Hg) is the only metal that is already liquid at room temperature, with a melting point of −39 °C.
❌ Why the other options are incorrect
✗ Copper and cobalt — both are hard, high-melting transition metals; Cu melts at 1085 °C and Co at 1495 °C.
✗ Zinc and copper — zinc melts at 420 °C (low for a metal, but far above room temperature) and copper at 1085 °C. This pair forms the alloy brass.
✗ Iron and nickel — Fe melts at 1538 °C and Ni at 1455 °C; both are used precisely because they stay solid at high temperatures.
📌 SSC & Railway Exam Facts
• Mercury — the only metal liquid at room temperature; bromine — the only non-metal liquid at room temperature.
• Tungsten (W) has the highest melting point among metals, 3422 °C, hence its use in bulb filaments.
• Carbon (diamond) is the hardest natural substance; graphite conducts electricity.
• Sodium and potassium are so soft they can be cut with a knife.
• Brass = Cu + Zn, Bronze = Cu + Sn, Stainless steel = Fe + Cr + Ni.

Correct Answer: Option 4 — Fe
A metal reacts with a dilute acid only if it lies above hydrogen in the reactivity series, displacing H⁺ to liberate hydrogen gas. The higher a metal stands in the series, the more vigorous the reaction.
The relevant order in the activity series is:
Mg > Al > Zn > Fe > (H) > Cu
Among the four metals given, iron (Fe) sits lowest, immediately above hydrogen. It therefore reacts with dilute HCl most slowly — the effervescence is gentle and the solution slowly turns pale green, whereas magnesium reacts almost explosively.
⚗️ The Reactions
Mg + 2HCl → MgCl₂ + H₂↑ — very vigorous, the test tube becomes hot
2Al + 6HCl → 2AlCl₃ + 3H₂↑ — vigorous once the oxide layer dissolves
Zn + 2HCl → ZnCl₂ + H₂↑ — brisk, the standard laboratory method for making H₂
Fe + 2HCl → FeCl₂ + H₂↑ — the slowest of the four
❌ Why the other options are incorrect
✗ Zn — it lies above iron, so it reacts faster than Fe; zinc with dilute HCl is the usual laboratory preparation of hydrogen.
✗ Mg — the most reactive of the four; it reacts so fast that the mixture heats up strongly.
✗ Al — more reactive than both zinc and iron; it is protected only by a thin oxide layer, which the acid removes.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au > Pt.
• Metals below hydrogen — Cu, Ag, Au — do not displace H₂ from dilute acids.
• Dilute HNO₃ does not usually give H₂ with metals because it is a strong oxidising agent; Mg and Mn are the exceptions.
• Aqua regia (3 : 1 conc. HCl : conc. HNO₃) dissolves even gold and platinum.
• The burning splinter test — hydrogen burns with a pop sound.

Correct Answer: Option 4 — Zn + CuCl₂ → ZnCl₂ + Cu
The reactivity series arranges metals in decreasing order of their tendency to lose electrons:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au
The rule for a displacement reaction is simple: a more reactive metal displaces a less reactive metal from its salt solution. If the free metal is below the metal in the salt, no reaction takes place.
⚗️ The Reaction
Zn + CuCl₂ → ZnCl₂ + Cu
• Zinc is above copper in the series, so zinc displaces copper — the reaction is possible.
• The blue copper salt solution fades and reddish-brown copper is deposited.
• It is a redox change: Zn is oxidised to Zn²⁺ and Cu²⁺ is reduced to Cu.
❌ Why the other options are incorrect
✗ 3Cu + FeCl₃ → 3CuCl₂ + Fe — copper is below iron, so copper cannot displace iron; no reaction occurs.
✗ 3Ag + AlCl₃ → 3AgCl + Al — silver is far below aluminium; a very unreactive metal can never displace a very reactive one.
✗ Cu + ZnCl₂ → CuCl₂ + Zn — copper is below zinc, so this is impossible; it is the exact reverse of the correct reaction.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• A more reactive metal displaces a less reactive one from its salt solution.
• Fe + CuSO₄ → FeSO₄ + Cu: blue turns green, iron nail turns brown.
• Metals above hydrogen displace H₂ from dilute acids; Cu, Ag, Au do not.
• Potassium is the most reactive and gold the least reactive of the common metals.

Correct Answer: Option 2 — Table salt
An ionic (electrovalent) compound is formed by the complete transfer of electrons from a metal to a non-metal, producing oppositely charged ions held together by a strong electrostatic force.
Table salt is sodium chloride (NaCl). Sodium (Na) has 1 electron in its outermost shell and donates it to chlorine (Cl), which needs 1 electron to complete its octet. This gives Na⁺ and Cl⁻, which attract each other strongly and build a crystal lattice.
Because of this strong lattice, ionic compounds are hard, brittle solids with high melting and boiling points, are generally soluble in water but insoluble in kerosene or petrol, and conduct electricity in molten or aqueous state (not in the solid state, where the ions are not free to move).
❌ Why the other options are incorrect
✗ Sugar — sucrose (C₁₂H₂₂O₁₁) is a covalent compound; its molecules share electrons and its solution does not conduct electricity.
✗ Glucose — C₆H₁₂O₆ is likewise covalent, made of carbon, hydrogen and oxygen — all non-metals, so no electron transfer occurs.
✗ Turmeric — turmeric is not a single compound at all; it is a natural indicator that turns red in a basic solution.
📌 SSC & Railway Exam Facts
• Ionic compound = metal + non-metal, e.g. NaCl, MgCl₂, CaO, KBr.
• Ionic compounds conduct electricity in molten and aqueous state, not as solids.
• They have high melting and boiling points and are soluble in water, insoluble in petrol/kerosene.
• NaCl = common salt; raw material for NaOH, washing soda, baking soda and bleaching powder.
• Turmeric, litmus, red cabbage and China rose (hibiscus) are natural indicators.

Correct Answer: Option 2 — Gangue
An ore dug out of the earth is never pure — it is always mixed with earthy and rocky impurities such as sand, clay, limestone and mica. These unwanted impurities present in an ore are collectively called gangue (also called matrix).
Removing the gangue is the first step of metallurgy and is called concentration or dressing of the ore. It is done by hydraulic (gravity) washing, magnetic separation, froth flotation or chemical leaching, depending on the nature of the ore and the gangue.
Inside the furnace, a substance called flux is added to combine with the leftover gangue; the fusible product formed is called slag.
❌ Why the other options are incorrect
✗ Calcinations — this is the process of heating a carbonate ore strongly in the absence or limited supply of air to get the oxide: ZnCO₃ → (heat) ZnO + CO₂.
✗ Anode mud — the insoluble impurities (Ag, Au, Pt) that settle below the anode during electrolytic refining; they are impurities of a metal, not of an ore.
✗ Roasting — heating a sulphide ore strongly in excess of air: 2ZnS + 3O₂ → (heat) 2ZnO + 2SO₂; it is a process, not the name of an impurity.
📌 SSC & Railway Exam Facts
• Steps of metallurgy: concentration → roasting/calcination → reduction → refining.
• Gangue + flux = slag; CaCO₃ is the flux used in the blast furnace.
• Froth flotation is used for sulphide ores (e.g. ZnS, PbS, CuFeS₂).
• Bauxite (Al₂O₃·2H₂O) is concentrated by Bayer's leaching process using NaOH.
• Anode mud is an important commercial source of gold, silver and platinum.

Correct Answer: Option 1 — Potassium and gold
The reactivity series (activity series) arranges metals in the decreasing order of their tendency to lose electrons and form positive ions:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au
Potassium (K) stands at the very top, so it is the most reactive metal, while gold (Au) stands at the very bottom, so it is the least reactive. Hence *potassium and gold* is the pair representing the most and the least reactive metals.
Potassium is so reactive that it catches fire on contact with water and is stored under kerosene. Gold, being least reactive, occurs in the free (native) state, does not tarnish or corrode, and is therefore called a noble metal.
❌ Why the other options are incorrect
✗ Calcium and gold — gold is correctly the least reactive, but calcium lies below both potassium and sodium, so it is not the most reactive.
✗ Magnesium and gold — magnesium is only moderately reactive; it burns in air but does not react with cold water.
✗ Sodium and gold — sodium is very reactive, yet it still stands below potassium in the series.
📌 SSC & Railway Exam Facts
• Memory order: K Na Ca Mg Al Zn Fe Pb H Cu Hg Ag Au.
• K and Na are stored in kerosene because they react violently with air and water.
• Metals above hydrogen displace H₂ from dilute acids; Cu, Hg, Ag, Au do not.
• Au and Pt occur in the native (free) state; reactive metals occur as oxides, carbonates and sulphides.
• A more reactive metal displaces a less reactive one: Fe + CuSO₄ → FeSO₄ + Cu.

Correct Answer: Option 1 — Metal oxide
Air is a mixture in which the reactive component is oxygen (about 21%). When a metal is burnt in air, it combines with this oxygen to form a metal oxide:
Metal + O₂ → Metal oxide
2Mg + O₂ → (burning) 2MgO, 4Na + O₂ → 2Na₂O, 2Cu + O₂ → (heat) 2CuO
Most metal oxides are basic in nature — they dissolve in water to give alkalis (Na₂O + H₂O → 2NaOH) and react with acids to give salt and water. A few, such as Al₂O₃ and ZnO, react with both acids and bases and are called amphoteric oxides.
Highly reactive metals such as K and Na react so fast with the oxygen and moisture of air that they are kept immersed in kerosene.
❌ Why the other options are incorrect
✗ Metal chloride — formed when a metal reacts with chlorine or with hydrochloric acid (2Na + Cl₂ → 2NaCl), not with air.
✗ Metal nitrate — formed when a metal or its oxide reacts with nitric acid (HNO₃); air contains nitrogen as unreactive N₂, not as nitrate.
✗ Metal hydride — formed when a metal reacts with hydrogen (2Na + H₂ → 2NaH); air has almost no free hydrogen.
📌 SSC & Railway Exam Facts
• Air ≈ 78% N₂, 21% O₂, 0.9% Ar, 0.04% CO₂.
• Metal oxides are basic; non-metal oxides are acidic (CO₂, SO₂, NO₂).
• Amphoteric oxides: Al₂O₃, ZnO, PbO, SnO.
• Na and K are stored in kerosene; white phosphorus is stored in water.
• Aluminium forms a thin protective layer of Al₂O₃ that stops further corrosion.

Correct Answer: Option 1 — Copper
A displacement reaction takes place only when a more reactive metal displaces a less reactive metal from its salt solution. Whether a metal can do this is decided by its position in the reactivity series.
For the four metals given, the order of reactivity is:
Zinc (Zn) > Iron (Fe) > Lead (Pb) > Copper (Cu)
Copper lies lowest, so it cannot displace zinc, iron or lead from their salts — it is the least reactive of the four. On the contrary, all three of them can displace copper from copper sulphate solution.
⚗️ The Reaction
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
• The blue colour of CuSO₄ fades and a reddish-brown deposit of copper appears on the zinc.
• The reverse, Cu + ZnSO₄ → no reaction, proves copper is the less reactive metal.
❌ Why the other options are incorrect
✗ Lead — lead stands above copper in the series and can displace copper from CuSO₄, so it is not the least reactive.
✗ Iron and zinc — both are well above lead and copper; iron displaces copper (Fe + CuSO₄ → FeSO₄ + Cu) and zinc displaces both.
✗ Iron — iron is a moderately reactive metal that rusts readily and reacts with dilute acids; it is far more reactive than copper.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Metals below hydrogen (Cu, Hg, Ag, Au) do not release H₂ from dilute acids.
• Displacement: A + BC → AC + B, only if A is more reactive than B.
• Copper vessels are used for water because copper is unreactive; it turns green due to basic copper carbonate.
• Thermite reaction: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat, used to weld rail tracks.

Correct Answer: Option 1 — Potassium
The reactivity series (activity series) arranges metals in decreasing order of their reactivity, that is, of their tendency to lose electrons and form positive ions:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au
Potassium (K) stands at the very top of this series, so among the four options it is the most reactive metal. It reacts so violently with cold water that the hydrogen produced catches fire at once, and for this reason potassium is stored under kerosene.
The practical use of the series is simple: a metal higher in the list can displace any metal lower down from its salt solution — for example Zn + CuSO₄ → ZnSO₄ + Cu.
❌ Why the other options are incorrect
✗ Zinc — a moderately reactive metal placed below aluminium; it reacts with steam, not with cold water, and is far less reactive than potassium.
✗ Sodium — very reactive indeed and placed just below potassium, so it is highly reactive but not the most reactive among those given.
✗ Gold — the least reactive metal of all; it is found in the native (free) state and dissolves only in aqua regia.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au.
• Reactivity of metals increases down Group 1 and decreases across a period from left to right.
• K and Na are stored under kerosene; K, Na, Ca react with cold water, Mg with hot water, and Al, Zn, Fe with steam.
• Metals below hydrogen (Cu, Hg, Ag, Au) cannot displace hydrogen from dilute acids.
• A metal higher in the series displaces a lower one from its salt solution — the basis of all displacement reactions.

Correct Answer: Option 1 — Ductility
Ductility is the property of a metal by which it can be drawn into thin wires without breaking. It arises because the metallic bond allows layers of positive metal ions to slide over one another while the sea of delocalised electrons keeps holding them together.
Gold (Au) is the most ductile metal — one gram of gold can be drawn into a wire about 2 km long — followed by silver. Copper and aluminium are highly ductile too, which is why they are used for electrical wires.
Do not confuse it with malleability, the property of being beaten into thin sheets, in which gold and silver again lead, and by which aluminium foil is made for packing food.
❌ Why the other options are incorrect
✗ Neither malleability nor ductility — wrong, because drawing into wires is exactly the definition of ductility.
✗ Malleability — this is being hammered into sheets or foils, not wires; a very common confusion in exams.
✗ Both malleability and ductility — the question asks for a single specific property, wire-drawing, which is ductility alone.
📌 SSC & Railway Exam Facts
• Ductility → wires; Malleability → sheets/foils. Gold is the best in both.
• Non-metals are neither malleable nor ductile — they are brittle (except graphite, which is soft, and diamond, the hardest).
• Sonorous metals produce a ringing sound; that is why bells are made of metal.
• Mercury (Hg) is the only metal liquid at room temperature; bromine (Br₂) is the only liquid non-metal.
• Sodium (Na) and potassium (K) are so soft they can be cut with a knife.

Correct Answer: Option 2 — Hydrogen
Metals that lie above hydrogen in the reactivity series displace hydrogen from dilute acids, giving a salt and hydrogen gas. The general equation is
Metal + Dilute acid → Salt + Hydrogen gas
⚗️ The Reaction
Zn + 2HCl → ZnCl₂ + H₂↑
Mg + 2HCl → MgCl₂ + H₂↑
• This is a displacement reaction — the metal displaces H⁺ from the acid.
• The gas is confirmed by bringing a burning splinter near it: hydrogen burns with a pop sound.
Metals below hydrogen — such as copper, silver and gold — do not displace hydrogen and so give no reaction with dilute HCl. The vigour of the reaction follows the reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
❌ Why the other options are incorrect
✗ Oxygen — oxygen is released when hydrogen peroxide decomposes or at the anode during electrolysis of water, not from a metal–acid reaction.
✗ Chlorine — chlorine is obtained by electrolysis of brine (NaCl solution); the chloride ion stays in the salt here, it is not released as Cl₂.
✗ Nitrogen — nitrogen comes from the air or from nitrogenous compounds; HCl contains no nitrogen at all.
📌 SSC & Railway Exam Facts
• Metal + dilute acid → salt + H₂; the pop test with a burning splinter confirms hydrogen.
• Cu, Ag and Au are below hydrogen — they do not react with dilute HCl or dilute H₂SO₄.
• Nitric acid (HNO₃) normally does not give H₂, because it is a strong oxidising agent.
• Aqua regia = 3 parts conc. HCl + 1 part conc. HNO₃ — it dissolves gold and platinum.
• The reactivity series order: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.

Correct Answer: Option 2 — Magnesium (Mg) and manganese (Mn)
Nitric acid (HNO₃) is a strong oxidising agent. When a metal reacts with it, the hydrogen produced is normally oxidised straight to water, while the acid itself is reduced to nitrogen oxides (N₂O, NO, NO₂). That is why metals with HNO₃ usually give no hydrogen gas.
Magnesium (Mg) and manganese (Mn) are the standard exceptions given in NCERT: with very dilute nitric acid these two metals do evolve hydrogen gas, because the acid is too dilute to act effectively as an oxidiser.
⚗️ The Reaction
Mg + 2HNO₃ (very dilute) → Mg(NO₃)₂ + H₂↑
Mn + 2HNO₃ (very dilute) → Mn(NO₃)₂ + H₂↑
• The gas burns with a pop sound, the standard test for hydrogen.
❌ Why the other options are incorrect
✗ Copper (Cu) and cobalt (Co) — copper lies below hydrogen in the reactivity series and cannot displace hydrogen from any acid.
✗ Manganese (Mn) and cobalt (Co) — Mn is right, but cobalt is not one of the two textbook exceptions.
✗ Magnesium (Mg) and copper (Cu) — Mg is right, but copper cannot give H₂; with dilute HNO₃ copper gives NO, and with concentrated HNO₃ it gives NO₂.
📌 SSC & Railway Exam Facts
• Only Mg and Mn give H₂ with very dilute HNO₃ — a classic one-liner.
• HNO₃ is a strong oxidising agent; it normally gives NO₂, NO or N₂O instead of H₂.
• Metals above hydrogen in the reactivity series displace H₂ from dilute HCl and dilute H₂SO₄.
• Aqua regia (3 HCl : 1 HNO₃) dissolves gold and platinum.
• Hydrogen is confirmed by the pop test; it is the lightest element and burns to give only water.

Correct Answer: Option 1 — anode mud
Electrolytic refining is the last step of metallurgy and gives the metal in a very pure (about 99.9%) form. The arrangement is fixed:
• Anode (+) — a thick block of the impure metal
• Cathode (−) — a thin strip of the pure metal
• Electrolyte — a water-soluble salt of the same metal (for copper, acidified CuSO₄ solution)
When current is passed, the impure metal at the anode dissolves into the electrolyte as ions and an equal amount of pure metal is deposited on the cathode. The impurities do not follow: the soluble impurities go into the solution, while the insoluble impurities fall below the anode as a sludge called anode mud (anode sludge).
This anode mud is commercially valuable — in copper refining it contains silver, gold, platinum and selenium, which are recovered from it.
❌ Why the other options are incorrect
✗ gangue — the earthy, unwanted impurity present in the ore itself (sand, clay, rock), removed during concentration of the ore, long before refining begins.
✗ electrolytic mud — not a standard chemistry term; the accepted name for the deposit under the anode is anode mud.
✗ cathode mud — nothing settles at the cathode; the cathode only gains a coating of pure metal and becomes thicker.
📌 SSC & Railway Exam Facts
• In electrolytic refining: anode = impure metal, cathode = pure metal, electrolyte = salt solution of that metal.
• The deposit below the anode is anode mud, a commercial source of Ag, Au and Pt.
• Copper, zinc, tin, nickel, silver, gold and aluminium are refined electrolytically.
• Roasting = heating a sulphide ore strongly in excess air; calcination = heating a carbonate ore in limited air.
• Impurity in an ore = gangue; the substance added to remove gangue as slag = flux.

Correct Answer: Option 2 — pure metal
In electrolytic refining, the impure metal obtained after reduction of the ore is purified by electrolysis. The set-up is fixed and is asked directly in exams:
• Anode (positive electrode) — a thick block of the impure metal
• Cathode (negative electrode) — a thin strip or sheet of the pure metal
• Electrolyte — an aqueous solution of a salt of the same metal, e.g. acidified CuSO₄ for copper
On passing current the anode dissolves — metal atoms lose electrons and enter the solution as ions (Cu → Cu²⁺ + 2e⁻) — and an equivalent amount of metal is reduced and deposited on the cathode (Cu²⁺ + 2e⁻ → Cu) in a very pure form. The insoluble impurities settle below the anode as anode mud.
So the cathode must be made of the pure metal; it keeps growing thicker as refining proceeds, while the anode gets thinner.
❌ Why the other options are incorrect
✗ impure metal — the impure metal is used as the anode, which dissolves away and becomes thinner during refining.
✗ alloy metal — an alloy would add fresh impurities to the deposit and defeat the very purpose of refining.
✗ metal salt — the salt is used as the electrolyte solution, not as an electrode; a solid salt is also a poor conductor of electricity.
📌 SSC & Railway Exam Facts
• Cathode = pure metal (reduction); anode = impure metal (oxidation).
• Electrode reactions: anode Cu → Cu²⁺ + 2e⁻; cathode Cu²⁺ + 2e⁻ → Cu.
• The anode mud below the anode contains valuable Ag, Au, Pt and Se.
• Reduction always occurs at the cathode and oxidation at the anode.
• Order of metallurgy: concentration of ore → roasting/calcination → reduction → refining.

Correct Answer: Option 4 — Aluminium
How a metal behaves with water depends entirely on its position in the reactivity series:
• Very reactive metals (K, Na, Ca) react with cold water.
• Magnesium does not react with cold water but does react with hot water.
• Aluminium, zinc and iron react only with steam, not with cold or hot water.
• Copper, silver and gold do not react with water at all.
Aluminium therefore matches the question exactly. With steam it gives aluminium oxide and hydrogen gas.
⚗️ The Reaction
2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g)
• The water must be in the gaseous (steam) state, shown by the (g).
• A metal oxide — not a hydroxide — is formed, because the hydroxide cannot survive the temperature of steam.
• Compare: 2Na + 2H₂O → 2NaOH + H₂ (cold water) and Mg + 2H₂O → Mg(OH)₂ + H₂ (hot water).
❌ Why the other options are incorrect
✗ Potassium — the most reactive of the four; it reacts violently with cold water, and the hydrogen released catches fire at once.
✗ Sodium — also reacts vigorously with cold water to give NaOH and H₂; it is stored under kerosene for this reason.
✗ Magnesium — it does not react with cold water but does react with hot water to give Mg(OH)₂, so it is not a "steam only" metal.
📌 SSC & Railway Exam Facts
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au.
• Na and K are stored under kerosene to keep them away from air and moisture.
• Metals below hydrogen (Cu, Hg, Ag, Au) cannot displace hydrogen from dilute acids.
• Aluminium resists corrosion because a thin protective layer of Al₂O₃ forms on its surface.
• Gold and platinum are the least reactive metals and occur in the native (free) state.

Correct Answer: Option 1 — Gold
Metals lying at the bottom of the reactivity series are so unreactive that they do not combine with the oxygen, moisture or other elements present in the earth's crust. They are therefore found uncombined, that is, in the free or native state. Gold, silver and platinum (and partly copper) are the metals found this way.
Gold (Au) is the classic example — it is the least reactive common metal, it does not tarnish in air, it is not attacked by water or by ordinary acids, and it dissolves only in aqua regia (a 3 : 1 mixture of conc. HCl and conc. HNO₃). Because of this inertness, nuggets of pure gold occur naturally in rocks and river beds.
Metals higher up the series are too reactive to survive uncombined and always occur as oxides, sulphides or carbonates, i.e. as ores, which must be reduced to obtain the metal.
❌ Why the other options are incorrect
✗ Zinc — a moderately reactive metal; it occurs as zinc blende (ZnS) and calamine (ZnCO₃), never in the free state.
✗ Aluminium — highly reactive; found as bauxite (Al₂O₃·2H₂O) and extracted only by electrolysis of molten alumina.
✗ Sodium — one of the most reactive metals of all; it reacts violently even with cold water, so it cannot exist free and is stored under kerosene.
📌 SSC & Railway Exam Facts
• Metals found in the native/free state: gold, silver, platinum and partly copper.
• Aqua regia = 3 parts conc. HCl + 1 part conc. HNO₃; it dissolves gold and platinum.
• The purity of gold is measured in carats; 24-carat gold is pure, ornaments are made of 22-carat.
• Highly reactive metals (K, Na, Ca, Mg, Al) are obtained by electrolytic reduction.
• Important ores: bauxite (Al), haematite (Fe₂O₃), zinc blende (ZnS), cinnabar (HgS), copper pyrites (CuFeS₂).

Correct Answer: Option 4 — Liquid state
Bromine (Br), atomic number 35, belongs to Group 17 — the halogens. It is the only non-metal that is a liquid at room temperature — a dense, reddish-brown, fuming liquid with a sharp, choking smell (its name comes from the Greek *bromos*, meaning "stench"). Its melting point is −7.2 °C and its boiling point is 58.8 °C.
Most non-metals are either gases (hydrogen, nitrogen, oxygen, fluorine, chlorine and the noble gases) or brittle solids (carbon, sulphur, phosphorus, iodine). Bromine is the single liquid exception among the non-metals, just as mercury (Hg) is the single liquid exception among the metals — a pairing asked again and again in exams.
❌ Why the other options are incorrect
✗ Plasma state — plasma is the fourth state of matter, a super-heated ionised gas found in the Sun, stars and fluorescent tubes; it is not the ordinary state of bromine.
✗ Solid state — the solid non-metals are iodine, sulphur, phosphorus and carbon; bromine is not solid at room temperature (it freezes only below −7.2 °C).
✗ Gaseous state — bromine fumes and vapourises easily, which is misleading, but at 25 °C it is definitely a liquid; fluorine and chlorine are the gaseous halogens.
📌 SSC & Railway Exam Facts
• Bromine is the only liquid non-metal; mercury is the only liquid metal at room temperature.
• Gallium (≈30 °C) and caesium (≈28 °C) are metals that melt with the heat of the palm.
• Halogens (Group 17): F₂ and Cl₂ are gases, Br₂ is a liquid, I₂ and At are solids.
• Iodine is the non-metal with a metallic lustre; graphite is the non-metal that conducts electricity.
• Diamond, an allotrope of carbon, is the hardest natural substance known.

Correct Answer: Option 3 — Gold and platinum
The reactivity series arranges metals in decreasing order of their tendency to lose electrons:
K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au
Metals at the bottom of this series are so unreactive that they do not combine with the oxygen, water or other elements present in the earth's crust. They are therefore found uncombined — in the native or free state. Gold (Au) and platinum (Pt) are the two most typical examples; silver and partly copper are also found free.
Gold does not tarnish, is unaffected by water and by dilute acids, and dissolves only in aqua regia (conc. HCl : conc. HNO₃ = 3 : 1). Platinum is equally inert, which is why it is used for laboratory electrodes and crucibles.
❌ Why the other options are incorrect
✗ Sodium and potassium — the most reactive metals of the series; they react violently even with cold water and are stored under kerosene, so they can never occur free.
✗ Calcium and aluminium — both are highly reactive; calcium occurs as limestone (CaCO₃) and gypsum (CaSO₄·2H₂O), aluminium as bauxite, and both are obtained by electrolytic reduction.
✗ Calcium and magnesium — both reactive metals found as carbonates and sulphates; magnesium even burns in air with a dazzling white flame.
📌 SSC & Railway Exam Facts
• Native/free-state metals: gold, silver and platinum (and partly copper).
• Aqua regia = conc. HCl : conc. HNO₃ = 3 : 1; it dissolves gold and platinum.
• Highly reactive metals (K, Na, Ca, Mg, Al) are extracted by electrolytic reduction.
• Moderately reactive metals (Zn, Fe, Pb, Cu) are extracted by roasting/calcination followed by reduction with carbon.
• In the standard series the most reactive metal is potassium and the least reactive is gold.

Answer: Option 2 — Iron
Iron is more reactive than copper, so it displaces copper from copper sulphate solution.
Fe + CuSO_(4) → FeSO_(4) + Cu
Revision note — Reactivity series and displacement (Class 10)
• A more reactive metal displaces a less reactive metal from its salt solution.
• Order: K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au (Pt at the bottom).
• Iron nail in blue CuSO_(4): a reddish-brown copper coating forms and the solution turns pale green (FeSO_(4)).
• Zinc also displaces copper: Zn + CuSO_(4) → ZnSO_(4) + Cu.
• Silver, gold and platinum lie below copper, so they cannot displace it.
• Metals below hydrogen (Cu, Ag, Au) do not give H_(2) with dilute acids.
Also asked from this topic: the colour of the deposit on an iron nail in copper sulphate solution (reddish-brown copper); why lead cannot displace iron from iron(II) sulphate (lead is less reactive than iron).

Answer: Option 1 — Lead nitrate and silver nitrate
A metal displaces only a less reactive metal from its salt solution.
Zinc is above lead and silver but below aluminium in the reactivity series.
Revision note — Reactivity series and displacement
• Order (NCERT): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• Zn + Pb(NO_(3))_(2) → Zn(NO_(3))_(2) + Pb; Zn + 2AgNO_(3) → Zn(NO_(3))_(2) + 2Ag.
• Zn + Al_(2)(SO_(4))_(3) → no reaction — aluminium is more reactive than zinc.
• Fe + CuSO_(4) → FeSO_(4) + Cu — the blue solution turns light green.
• Metals above hydrogen release H_(2) from dilute acids; Cu, Ag, Au do not.
• Cu + 2AgNO_(3) → Cu(NO_(3))_(2) + 2Ag — the solution turns blue.
Also asked from this topic: what happens when a zinc strip is dipped in iron(II) sulphate (zinc displaces iron); why lead does not react with iron(II) sulphate (lead is less reactive than iron).

Answer: Option 1 — C
A metal can displace another from its salt solution only if it is more reactive.
The clues give C > A, A > B and B > D, so the order is C > A > B > D and C is the most reactive.
Revision note — Reactivity series and displacement
• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au.
• A more reactive metal displaces a less reactive metal from its salt solution — a displacement reaction.
• Fe + CuSO_(4) → FeSO_(4) + Cu: the blue solution turns pale green and reddish-brown copper coats the iron nail.
• Metals above hydrogen displace H_(2) from dilute acids; Cu, Ag, Au (below hydrogen) do not.
• K and Na are so reactive they are stored under kerosene; gold and platinum occur free (native) in nature.
Also asked from this topic: the most reactive of P, Q, R, S when each displaces the next (P); why lead cannot displace iron (lead is less reactive).

Answer: Option 4 — Magnesium
The more reactive the metal, the faster it displaces hydrogen from a dilute acid.
Of the four, magnesium is the highest in the reactivity series, so it bubbles fastest.
Mg + H_(2)SO_(4) → MgSO_(4) + H_(2)↑
Revision note — Reactivity series and acids
• Order to remember: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
• For these options: Mg > Al > Zn > Fe — so the speed of bubbling falls in the same order.
• Only metals above hydrogen release H_(2) gas with dilute acids; Cu, Ag, Au do not.
• Metal + dilute acid → salt + hydrogen; hydrogen burns with a pop sound.
• Aluminium starts slowly because of its protective oxide layer (Al_(2)O_(3)).
• Nitric acid usually does not give H_(2) (it is an oxidising agent) — except Mg and Mn with very dilute HNO_(3).
Do not mix these up
• Aluminium vs magnesium — Al is below Mg in the series, and its oxide coat slows it further.
Also asked from this topic: which metals do not give hydrogen with dilute acids (those below hydrogen, like Cu, Ag, Au); the product formed with hydrogen when a metal reacts with an acid (salt).

Answer: Option 3 — black; green
Silver reacts with sulphur compounds in air to form a black coat of silver sulphide (Ag_(2)S).
Copper reacts with moist CO_(2) in air to form a green coat of basic copper carbonate.
Revision note — Corrosion of metals
• Corrosion — a metal is slowly eaten away by air, moisture or chemicals around it.
• Iron → reddish-brown rust, hydrated iron(III) oxide Fe_(2)O_(3)·xH_(2)O; needs both air and water.
• Silver → black (Ag_(2)S, from H_(2)S in air).
• Copper → green (CuCO_(3)·Cu(OH)_(2), basic copper carbonate).
• Prevention: painting, oiling, greasing, galvanising (zinc coat), chrome plating, anodising, alloying.
• Gold and platinum do not corrode — they are the least reactive.
Do not mix these up
• Copper heated in air vs copper left in moist air — heating gives black copper(II) oxide; slow corrosion gives a green coat.
Also asked from this topic: why silver articles turn black (a silver sulphide coating forms); the name of the gradual eating away of metals (corrosion).

Answer: Option 3 — Potassium
Potassium (K) loses its outer electron most easily, so it heads the reactivity series.
Revision note — Reactivity series of metals
• Order: K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au.
• Most reactive: potassium; least reactive: gold (with platinum).
• K and Na react violently with cold water — the hydrogen catches fire; they are stored under kerosene.
• A more reactive metal displaces a less reactive one from its salt solution: Fe + CuSO_(4) → FeSO_(4) + Cu.
• Metals above hydrogen give H_(2) with dilute acids; Cu, Hg, Ag, Au do not.
• Metals low in the series (Au, Ag, Pt) occur free in nature; top metals (K, Na, Ca, Mg, Al) are extracted by electrolysis.
Also asked from this topic: the metal that reacts violently with cold water and the hydrogen catches fire (potassium); what a displacement reaction shows (the solid metal is more reactive than the metal in solution).

Answer: Option 2 — Ionic bonds prevent ion movement in solid KBr.
In solid KBr the K⁺ and Br⁻ ions are locked in a rigid crystal lattice by strong electrostatic attraction.
Electricity needs moving charges; on melting the lattice breaks and the ions become free to move.
Revision note — Properties of ionic compounds
• Formed by transfer of electrons from a metal to a non-metal (e.g. NaCl, KBr, MgCl_(2), CaO).
• Hard solids, but brittle — they break into pieces under pressure.
• High melting and boiling points — much energy is needed to break the strong interionic attraction (NaCl melts at 801 °C).
• Soluble in water, insoluble in kerosene and petrol.
• Conduct electricity only in molten state or aqueous solution, never as solids.
• Charge is carried by ions here, whereas in metals it is carried by free electrons.
Do not mix these up
• Ionic compound vs metal — solid copper conducts through free electrons; solid KBr has no mobile charge at all.
Also asked from this topic: why sodium chloride is a solid at room temperature (strong electrostatic attraction between ions); a property common to ionic compounds (high melting and boiling points).

Answer: Option 4 — Copper
Corrosion is faster for more reactive metals.
Of the four, copper is lowest in the reactivity series (Mg > Zn > Fe > Cu), so it corrodes least.
Revision note — Corrosion of metals
• Corrosion — slow eating away of a metal by air, moisture or chemicals on its surface.
• Iron → rust, a reddish-brown hydrated iron(III) oxide, Fe_(2)O_(3)·xH_(2)O; rusting needs both air (oxygen) and water.
• Copper → slowly loses its shine and gets a green coat of basic copper carbonate (moist CO_(2) in air).
• Silver → turns black (silver sulphide, from sulphur in air).
• Prevention: painting, oiling, greasing, galvanising, chrome-plating, anodising and making alloys.
• Galvanisation — coating iron with zinc; zinc, being more reactive, corrodes first and protects the iron.
• Gold and platinum hardly corrode at all — they are the least reactive metals.
Do not mix these up
• Zinc vs copper — zinc is more reactive than iron and is used to protect iron; copper is less reactive and corrodes only slowly on its own.
Also asked from this topic: the colour of the layer formed on copper in moist air (green); the chemical in rust (hydrated iron(III) oxide, Fe_(2)O_(3)·xH_(2)O).

Answer: Option 2 — loses one electron
Sodium has the configuration 2, 8, 1 — it gives up its single outer electron to become Na^(+) (2, 8).
Chlorine (2, 8, 7) takes that electron and becomes Cl^(−) (2, 8, 8).
Revision note — Formation of ionic compounds
• An ionic (electrovalent) bond forms by transfer of electrons from a metal to a non-metal.
• The metal forms a cation (positive ion); the non-metal forms an anion (negative ion).
• Both ions reach a stable octet (noble-gas configuration): Na^(+) like neon, Cl^(−) like argon.
• The ions are held by strong electrostatic attraction.
• Ionic compounds are hard solids with high melting and boiling points, dissolve in water, and conduct electricity only when molten or in solution.
• Protons never move in a chemical reaction — only electrons are gained, lost or shared.
Do not mix these up
• Ionic vs covalent bond — ionic bonds transfer electrons (NaCl, MgCl_(2)); covalent bonds share electron pairs (H_(2)O, CO_(2), NH_(3)).
Also asked from this topic: a compound formed by ionic bonding (NaCl); the bond between a metal and a non-metal (ionic bond).