RRB JE CBT-1 2024-25 18 December 2024 Shift 2 GK Questions – with answers & solutions

Answer: Option 2 — basic
Sodium carbonate is the salt of a strong base (NaOH) and a weak acid (H₂CO₃).
In water it hydrolyses and gives OH⁻ ions, so the solution has pH above 7 — it is basic.
Revision note — Nature of salt solutions
• Strong acid + strong base → neutral salt, pH 7; e.g. NaCl, Na₂SO₄, KNO₃.
• Strong acid + weak base → acidic salt, pH below 7; e.g. NH₄Cl, CuSO₄.
• Weak acid + strong base → basic salt, pH above 7; e.g. Na₂CO₃, NaHCO₃, CH₃COONa.
• Washing soda = Na₂CO₃·10H₂O (10 water of crystallisation); used in glass, soap, paper industries and to remove permanent hardness of water.
• Baking soda = NaHCO₃ — mildly basic, used as an antacid and in soda-acid fire extinguishers.
• Na₂CO₃ turns red litmus blue and phenolphthalein pink.
Do not mix these up
• Washing soda vs baking soda — Na₂CO₃·10H₂O is washing soda; NaHCO₃ is baking soda.
Also asked from this topic: the nature of NaCl solution (neutral); the salt among NH₄Cl, Na₂CO₃ and sodium acetate that gives an acidic solution (NH₄Cl); the salt type that gives pH 9 (strong base + weak acid).

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 3 — ester
Ethanol (an alcohol) reacts with acetic acid (ethanoic acid) in the presence of an acid to form a sweet-smelling ester and water.
This reaction is called esterification.
Revision note — Ethanol, ethanoic acid and esters
• Esterification: CH_(3)COOH + C_(2)H_(5)OH → CH_(3)COOC_(2)H_(5) + H_(2)O, catalysed by conc. H_(2)SO_(4).
• The product ethyl ethanoate (ethyl acetate) is an ester with a fruity, sweet smell — used in perfumes and flavouring agents.
• Saponification: an ester + NaOH gives back the alcohol and the sodium salt of the acid — the reaction used to make soap.
• Ethanoic acid is commonly called acetic acid; a 5–8% solution in water is vinegar.
• Pure ethanoic acid freezes at 290 K in cold climates, so it is called glacial acetic acid.
• Ethanol + sodium gives hydrogen gas and sodium ethoxide.
Do not mix these up
• Ethanal vs ethanoate — ethanal (CH_(3)CHO) is the aldehyde formed by oxidising ethanol; an ethanoate is the ester or salt of ethanoic acid.
Also asked from this topic: the type of reaction between ethanoic acid and ethanol with an acid catalyst (esterification).
"Acetate" alone is only a part of the name — the class of compound formed is an ester.

Answer: Option 3 — pH = 7
When [H^(+)] = [OH^(−)], the solution is neutral.
At 25 °C, each concentration is 10^(−7) mol/L, so pH = 7.
Revision note — The pH scale
• pH = −log[H^(+)]; scale runs from 0 to 14 (Sørensen).
• pH < 7 acidic, pH = 7 neutral, pH > 7 basic.
• Each unit of pH is a 10-fold change in [H^(+)].
• Common values: gastric juice about 1.2, lemon juice about 2.2, pure water 7, blood about 7.4, milk of magnesia about 10.
• Tooth decay starts when mouth pH falls below 5.5.
• Universal indicator shows different colours at different pH values.
Also asked from this topic: the substance that is neutral on the pH scale (pure water); the pH effect of a higher H^(+) concentration (lower pH); the nature of the salt of a strong acid and strong base (neutral).
Neutral means equal H^(+) and OH^(−), not zero of either.

Answer: Option 3 — A + B → AB
In a combination reaction, two or more reactants combine to form a single product.
So its general form is A + B → AB.
Revision note — Types of chemical reactions
• Combination: A + B → AB — e.g. CaO + H_(2)O → Ca(OH)_(2) (quicklime to slaked lime, exothermic).
• Decomposition: AB → A + B — by heat (CaCO_(3)), electricity (water) or light (AgCl, AgBr).
• Displacement: A + BC → AC + B — e.g. Fe + CuSO_(4) → FeSO_(4) + Cu (blue colour fades).
• Double displacement: AB + CD → AD + CB — e.g. Na_(2)SO_(4) + BaCl_(2) gives a white BaSO_(4) precipitate.
• Burning of coal and formation of water from H_(2) and O_(2) are also combination reactions.
Do not mix these up
• Combination vs decomposition — combination makes one product from many; decomposition breaks one reactant into many. Their general forms are exact reverses.
Also asked from this topic: the type of reaction CaO + H_(2)O → Ca(OH)_(2) + heat (combination reaction); the observation that confirms a combination reaction (only one new substance is produced).
Look at the right-hand side — a single product means combination.

Answer: Option 2 — Chlorine gas and dry calcium hydroxide
Bleaching powder is made by passing chlorine gas over dry slaked lime (calcium hydroxide).
Ca(OH)_(2) + Cl_(2) → CaOCl_(2) + H_(2)O
Revision note — Bleaching powder
• Chemical name calcium oxychloride; formula CaOCl_(2).
• The chlorine comes from the chlor-alkali process — electrolysis of brine gives NaOH, Cl_(2) (at the anode) and H_(2) (at the cathode).
• It bleaches by releasing chlorine, which acts as an oxidising agent.
• Uses: bleaching cotton and linen (textiles), wood pulp (paper), washed clothes (laundry).
• Also used to disinfect drinking water and as an oxidising agent in chemical industries.
Do not mix these up
• Bleaching powder CaOCl_(2) · baking soda NaHCO_(3) · washing soda Na_(2)CO_(3)·10H_(2)O · plaster of Paris CaSO_(4)·½H_(2)O.
Also asked from this topic: the gas that makes it bleach (chlorine); a use of bleaching powder besides bleaching (disinfecting drinking water); the name of the electrolysis of brine (chlor-alkali process).

Answer: Option 4 — Milk of magnesia
Acidity is caused by excess hydrochloric acid in the stomach.
An antacid is a mild base that neutralises this acid; milk of magnesia is a suspension of magnesium hydroxide, Mg(OH)_(2).
Revision note — Antacids and neutralisation
• Acid + base → salt + water is neutralisation.
• The stomach makes hydrochloric acid (HCl); too much of it causes indigestion / acidity.
• Common antacids: milk of magnesia (Mg(OH)_(2)), baking soda (NaHCO_(3)), aluminium hydroxide.
• Antacids must be mild bases — strong alkalis like NaOH or quick lime (CaO) would burn the gut.
• Other neutralisation uses: baking soda / calamine on an ant or bee sting (formic acid); quick lime or slaked lime for acidic soil.
Do not mix these up
• Lime water vs quick lime — lime water is a solution of Ca(OH)_(2) used to test CO_(2); quick lime is CaO. Neither is used as an antacid.
Also asked from this topic: how antacids relieve indigestion (by neutralising excess stomach acid); a kitchen substance that acts as an antacid (baking soda).

Answer: Option 1 — 10
Washing soda is sodium carbonate decahydrate, Na_(2)CO_(3)·10H_(2)O.
Deca = ten, so each formula unit carries 10 molecules of water of crystallisation.
Revision note — Common salts and water of crystallisation
• Washing soda: Na_(2)CO_(3)·10H_(2)O — made by recrystallising sodium carbonate; heating gives soda ash (anhydrous Na_(2)CO_(3)).
• Blue vitriol (copper sulphate): CuSO_(4)·5H_(2)O — turns white on heating as it loses water.
• Gypsum: CaSO_(4)·2H_(2)O; Plaster of Paris: CaSO_(4)·½H_(2)O.
• Baking soda: NaHCO_(3) — no water of crystallisation.
• Uses of washing soda: glass, soap and paper industries, making borax, household cleaning, removing permanent hardness of water.
Do not mix these up
• Washing soda vs baking soda — Na_(2)CO_(3)·10H_(2)O (sodium carbonate) vs NaHCO_(3) (sodium hydrogencarbonate).
Also asked from this topic: industries that use washing soda (glass, soap and paper); the chemical name of baking soda (sodium bicarbonate); calcium sulphate hemihydrate (Plaster of Paris).

Answer: Option 1 — sodium bicarbonate
Baking soda is sodium hydrogencarbonate (sodium bicarbonate), NaHCO_(3).
Revision note — Baking soda
• Made from NaCl + H_(2)O + CO_(2) + NH_(3) → NH_(4)Cl + NaHCO_(3).
• On heating: 2NaHCO_(3) → Na_(2)CO_(3) + H_(2)O + CO_(2) — the CO_(2) makes cakes rise.
• Baking powder = baking soda + a mild edible acid such as tartaric acid.
• It is a mild base — used as an antacid and in soda-acid fire extinguishers.
• Its solution is basic; it is not corrosive.
Do not mix these up
• Sodium bicarbonate vs sodium carbonate — baking soda is NaHCO_(3); Na_(2)CO_(3) is soda ash / washing soda.
• Magnesium hydroxide is milk of magnesia; calcium carbonate is limestone / chalk / marble.
Also asked from this topic: why baking soda is used in fire extinguishers (it releases carbon dioxide easily with acid); the gas needed with ammonia to make it (carbon dioxide).

Answer: Option 1 — Fertilisation
The fusion of the male gamete (from the pollen) with the female gamete (egg in the ovule) is fertilisation; it forms the zygote.
Revision note — Sexual reproduction in flowering plants
• Pollination: transfer of pollen from anther to stigma — comes before fertilisation.
• Self-pollination = same flower or plant; cross-pollination = another plant (by wind, water, insects, birds).
• The pollen grows a pollen tube through the style to reach the ovule in the ovary.
• Fertilisation happens inside the ovule; zygote → embryo.
• After fertilisation: ovule → seed, ovary → fruit; petals, sepals, stamens usually wither.
• Germination = seed growing into a seedling; propagation = producing new plants (e.g. vegetative propagation by stem, root, leaf).
Do not mix these up
• Pollination vs fertilisation — pollination moves pollen to the stigma; fertilisation fuses the gametes.
Also asked from this topic: the analogy Pollination : transfer of pollen :: Fertilisation : ? (fusion of gametes); what gametes are (haploid reproductive cells that fuse to form a zygote).

Answer: Option 3 — Planaria
In regeneration, a fully formed organism is cut into pieces and each piece grows into a complete organism.
Planaria and Hydra show this; it is carried out by specialised cells that divide and differentiate.
Revision note — Modes of asexual reproduction
• Binary fission: Amoeba, Paramecium, bacteria; Leishmania divides in a definite plane.
• Multiple fission: Plasmodium (malaria parasite).
• Budding: Yeast and Hydra — a bud grows out and detaches.
• Fragmentation: Spirogyra — the body simply breaks into pieces, each grows.
• Spore formation: Rhizopus (bread mould) — spores in sporangia.
• Vegetative propagation: Bryophyllum (buds on leaf margins), potato, rose, banana, sugarcane.
• All asexual modes involve one parent and no fusion of gametes.
Do not mix these up
• Regeneration vs fragmentation — in regeneration the organism has to be cut, and specialised cells rebuild it; in fragmentation the body breaks up on its own at maturity.
Also asked from this topic: what Amoeba, yeast and Hydra reproducing with one parent shows (no fusion of gametes); the incorrect statement on vegetative propagation (new plants from seed-bearing structures).
Hydra does both — budding and regeneration — but yeast only buds.

Answer: Option 1 — It allows plants to adapt to changing environmental conditions.
Variation gives some individuals traits that help them survive a change in the environment (heat, drought, disease).
These survivors reproduce, so variation is the raw material for evolution.
Revision note — Heredity and variation
• Heredity: passing of traits from parents to offspring; variation: differences among individuals of a species.
• The study of heredity and variation is genetics.
• Sexual reproduction produces more variation — genes from two parents combine, and meiosis shuffles them.
• Asexual reproduction gives very little variation — only from small errors in DNA copying.
• Variants suited to the environment are kept by natural selection (Darwin).
• Example: bacteria that can withstand heat survive a heat wave better.
Also asked from this topic: the study of heredity and variation (genetics); the process that makes siblings of the same parents look different (meiosis).
Identical offspring are the opposite of variation — that is what asexual reproduction tends to produce.

Answer: Option 2 — Meiosis
Reproductive cells (gametes) are made by meiosis, a reduction division.
It halves the chromosome number, so each gamete carries half the DNA of a body cell.
Revision note — Mitosis and meiosis
• Mitosis — in body (somatic) cells; gives 2 identical daughter cells with the same chromosome number; used for growth and repair.
• Meiosis — in reproductive organs (testes, ovaries, anthers, ovules); gives 4 daughter cells with half the chromosome number (haploid, n).
• Humans: body cells 46 chromosomes (2n); sperm and egg 23 each (n).
• At fertilisation two haploid gametes fuse, restoring 2n in the zygote — so the DNA amount stays constant across generations.
• Crossing over and random sorting in meiosis create variation among offspring.
Do not mix these up
• Cytokinesis is only the splitting of the cytoplasm at the end of a division; amitosis is direct division with no spindle.
Also asked from this topic: the number of daughter cells formed in meiosis (four); the name of reproductive cells formed by meiosis (gametes); why siblings look different (meiosis).

Answer: Option 2 — in any plane
Amoeba has no fixed shape and no fixed structure to guide the split.
So during binary fission its body can divide in any plane.
Revision note — Fission and other asexual methods
• Binary fission — one cell splits into two: Amoeba, Paramecium, bacteria.
• Leishmania (causes kala-azar) splits in a definite orientation, set by its whip-like flagellum.
• Multiple fission — one cell splits into many: Plasmodium (malarial parasite).
• Budding — Hydra, yeast; fragmentation — Spirogyra; spore formation — Rhizopus (bread mould).
• Regeneration — a whole body grows from a piece: Planaria, Hydra.
• All these involve a single parent and no gametes; offspring are near copies of the parent.
Do not mix these up
• Amoeba vs Leishmania — Amoeba splits in any plane; Leishmania in a definite plane related to its flagellum.
Also asked from this topic: what Amoeba, yeast and Hydra reproducing with one parent shows (asexual reproduction occurs without fusion of gametes).

Answer: Option 4 — Growth of a new plant from a cutting
A piece of stem (a cutting) grows new roots and shoots and rebuilds a whole plant.
Regrowing a complete body from a part is regeneration; in plants it is used as vegetative propagation.
The other three are not plants at all.
Revision note — Vegetative propagation
• New plants grow from roots, stems or leaves of one parent — no seeds, no gametes.
• Stem cutting — rose, sugarcane, money plant; layering — jasmine; grafting — mango, citrus.
• Leaf buds — Bryophyllum grows new plants from notches on its leaf margins.
• Plants such as banana, orange, rose, jasmine that have lost the capacity to make seeds are grown this way.
• Offspring are genetically identical to the parent, and the plant bears flowers and fruits sooner than one raised from seed.
• Tissue culture — many plants from a few cells of the growing tip; used for orchids and ornamentals.
Do not mix these up
• Regeneration vs budding — in regeneration a cut piece grows into a whole body (Planaria); in budding an outgrowth detaches from an intact parent (Hydra).
Also asked from this topic: why cutting, grafting and layering are used by gardeners (they produce genetically identical plants).

Answer: Option 2 — Genes
Mendel said each trait is controlled by a pair of 'factors' passed from parents to offspring.
These factors are now called genes.
Revision note — Mendel and heredity
• Gregor Johann Mendel — the Father of Genetics; worked on the garden pea, Pisum sativum, with 7 pairs of contrasting traits.
• Monohybrid cross (tall × short): F1 all tall; F2 3 : 1 (phenotype), 1 : 2 : 1 (genotype).
• Dihybrid cross F2 ratio: 9 : 3 : 3 : 1.
• Law of dominance, law of segregation, law of independent assortment.
• A gene is a segment of DNA on a chromosome; different forms of a gene are alleles.
• The word gene was coined by Wilhelm Johannsen (1909).
Do not mix these up
• Gene vs chromosome vs DNA — DNA is the chemical; a chromosome is a long DNA thread; a gene is one functional segment of it that controls a trait.
Also asked from this topic: the law that the two alleles separate during gamete formation (law of segregation); the genotype of a short pea plant (tt).

Answer: Option 1 — Tall
A cross of pure tall (TT) and pure short (tt) pea plants gives Tt plants in F1.
Tallness is dominant, so every F1 plant is tall — no medium or short plants appear.
Revision note — Mendel's monohybrid cross
• Gregor Mendel worked on the garden pea (Pisum sativum) and is the father of genetics.
• F1: all tall (Tt) — the trait that shows in F1 is dominant; the hidden one is recessive.
• F2 (selfing F1): phenotype 3 : 1 (tall : short), genotype 1 : 2 : 1 (TT : Tt : tt).
• The short trait reappears in F2, proving the recessive factor was not lost — it was only masked.
• Mendel studied 7 pairs of contrasting traits (height, seed shape, seed colour, flower colour …).
• Laws: law of dominance, law of segregation, law of independent assortment (dihybrid cross, F2 ratio 9 : 3 : 3 : 1).
Do not mix these up
• Dominance vs blending — F1 is fully tall, not medium; Mendel's result rejected the idea of blending.
Also asked from this topic: the genotype of a short pea plant (tt); the type of trait tallness is (dominant); the F2 phenotypic ratio of a monohybrid cross (3 : 1).

Answer: Option 2 — It allows rapid reproduction in favourable conditions.
Asexual reproduction needs only one parent and no gametes.
So a single-celled organism can simply divide again and again and build a large population quickly while food and conditions are good.
Revision note — Asexual reproduction
• One parent, no fusion of gametes, offspring are clones — nearly identical to the parent.
• Binary fission — Amoeba, Paramecium, bacteria; multiple fission — Plasmodium (malaria parasite).
• Budding — yeast, Hydra; fragmentation — Spirogyra; regeneration — Planaria, Hydra.
• Spore formation — Rhizopus (bread mould); spores have thick walls that survive bad conditions.
• Drawback: little variation, so a population is less able to survive a changed environment.
• Sexual reproduction needs two parents and increases variation — useful for evolution.
Do not mix these up
• Variation comes from sexual reproduction, not asexual — and needing a mate is a feature of sexual reproduction.
Also asked from this topic: what Amoeba, yeast and Hydra reproducing with one parent shows (asexual reproduction occurs without fusion of gametes).

Answer: Option 1 — Binary fission
In binary fission the single cell divides into two daughter cells.
Only a unicellular organism can do this — the whole body is one cell.
Revision note — Modes of asexual reproduction
• Binary fission: Amoeba (any plane), Leishmania (definite plane, due to its flagellum), Paramecium, bacteria.
• Multiple fission: one cell divides into many daughter cells — Plasmodium (malaria parasite).
• Fragmentation: a filament breaks into pieces that each grow — Spirogyra (multicellular).
• Regeneration: specialised cells rebuild the whole body from a piece — Planaria, Hydra.
• Budding: a bud grows on the parent — yeast (unicellular), Hydra (multicellular).
• Spore formation: sporangia release spores — Rhizopus (bread mould).
Do not mix these up
• Fragmentation vs regeneration — fragmentation is a normal way of reproducing (Spirogyra); regeneration rebuilds a body from any cut piece (Planaria) and needs specialised cells.
Also asked from this topic: the feature shown by Amoeba, yeast and Hydra reproducing with one parent (no fusion of gametes).

Answer: Option 3 — become zero
A series circuit has only one path for current. Removing or breaking any resistor opens the circuit, so no current flows.
Revision note — Series and parallel combinations
• Series: R = R₁ + R₂ + R₃; same current through each resistor; voltage divides.
• Equivalent resistance in series is greater than the largest resistor.
• Parallel: 1/R = 1/R₁ + 1/R₂ + 1/R₃; same voltage across each; current divides.
• Equivalent resistance in parallel is less than the smallest resistor.
• Household wiring is parallel — each appliance gets 220 V and works independently.
• Decorative serial bulb strings: one bulb fuses → all go off (series).
Do not mix these up
• Series vs parallel break — in series the whole circuit stops; in parallel only that branch stops, the rest keep working.
Also asked from this topic: the arrangement where removing one device does not stop the others (parallel); 4 Ω, 6 Ω and 12 Ω in parallel (2 Ω).

Answer: Option 2 — Straight and parallel
Inside a current-carrying solenoid the magnetic field is uniform, so its field lines are parallel straight lines.
Revision note — Magnetic field of a solenoid
• Solenoid: a coil of many circular turns of insulated wire wound close together in the shape of a cylinder.
• Its field pattern outside is like that of a bar magnet — one end acts as north, the other as south.
• Inside: field lines are straight and parallel — equal strength and direction at every point (uniform field).
• The field is stronger with more turns, larger current, and a soft-iron core.
• A soft-iron core inside a solenoid forms an electromagnet — a temporary magnet (used in electric bells, cranes, relays).
• Direction of the field: right-hand thumb rule (curl fingers along current; thumb gives the north end).
Do not mix these up
• Straight wire vs solenoid — a straight wire gives concentric circles; inside a solenoid the lines are parallel straight lines.
Also asked from this topic: the field pattern of a solenoid (parallel lines inside, closed loops outside); why a solenoid can magnetise soft iron (strong uniform field inside).

Answer: Option 3 — Snell's law
Snell's law links the bending of light to the ratio of its speeds in the two media: sin i / sin r = v₁ / v₂ = constant (the refractive index).
Revision note — Refraction of light
• Refraction: bending of light when it passes from one medium to another, because its speed changes.
• First law: incident ray, refracted ray and the normal lie in one plane.
• Second law (Snell's law): sin i / sin r = constant = refractive index of medium 2 w.r.t. medium 1.
• Refractive index n = c / v (speed in vacuum ÷ speed in the medium); n has no unit.
• Rarer → denser: ray bends towards the normal; denser → rarer: away from the normal.
• Examples: a pencil looks bent in water; a pool looks shallower; stars twinkle.
Do not mix these up
• Snell's law vs Huygens' principle — Snell's law is the refraction law; Huygens' principle is a wave construction used to derive it.
Also asked from this topic: the cause of light bending from air into water (change in speed); the law that incident ray, refracted ray and normal lie in one plane (first law of refraction).

Answer: Option 3 — Direction of motion
In Fleming's right-hand rule the thumb points along the motion of the conductor.
The rule gives the direction of the induced current in a conductor moving in a magnetic field.
Revision note — Fleming's right-hand rule (Class 10)
• Stretch the thumb, forefinger and middle finger of the right hand mutually perpendicular.
• Thumb → direction of motion of the conductor.
• Forefinger → direction of the magnetic field.
• Middle finger → direction of the induced current.
• Used for the electric generator (electromagnetic induction — mechanical energy → electrical energy).
Do not mix these up
• Right-hand vs left-hand rule — right-hand rule = generator (induced current).
Left-hand rule = motor (force on a current-carrying conductor).
Also asked from this topic: induced p.d. when a generator coil spins twice as fast (doubles); induced current for a conductor moving up in a north-to-south field (towards east).

Answer: Option 3 — is the same at all points
Inside a long current-carrying solenoid the field lines are parallel straight lines.
Parallel, equally spaced lines mean a uniform field — the same at every point inside.
Revision note — Magnetic field of a solenoid (Class 10)
• Solenoid = a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder.
• Its field pattern is like that of a bar magnet: one end acts as the north pole, the other as the south pole.
• Inside: parallel straight lines ⇒ uniform field; outside: lines loop from N to S.
• A strong uniform field inside can magnetise a soft iron piece placed in it — this makes an electromagnet.
• Field strength rises with more turns, larger current and a soft iron core.
Do not mix these up
• Solenoid vs circular loop — a single circular loop's field is strongest at its centre and not uniform; a solenoid's field is uniform inside.
Also asked from this topic: the shape of field lines inside a current-carrying solenoid (parallel straight lines); why a solenoid can magnetise soft iron (strong, uniform field inside).

Answer: Option 4 — Electric iron
An electric iron has a heating element of high resistance; current through it produces heat by Joule's law (H = I^(2)Rt).
The motor, generator and transformer work on magnetic effects of current, not on heating.
Revision note — Heating effect of electric current
• Joule's law: H = I^(2)Rt — heat ∝ square of current, ∝ resistance, ∝ time.
• Devices using heating: electric iron, heater, toaster, oven, geyser, kettle, bulb filament.
• Heating elements are made of nichrome — high resistivity and high melting point, does not oxidise easily.
• Bulb filaments are tungsten (melting point about 3380 °C); bulbs are filled with nitrogen and argon.
• A fuse works on the heating effect; its wire has a low melting point and is connected in series.
• Electric motor — magnetic force on a current-carrying conductor; generator — electromagnetic induction.
Also asked from this topic: why nichrome is used in heaters (high resistivity and high melting point); the change in heat when current is doubled (four times); the gas filled in electric bulbs (nitrogen and argon).
Transformer and generator also "get hot", but heat is their loss — the iron is the one built to use it.

Answer: Option 4 — Refraction in the Earth's atmosphere
Starlight passes through air layers whose temperature and density keep changing, so its refraction keeps changing.
The apparent position and brightness of the star flicker — this is twinkling, due to atmospheric refraction.
Revision note — Atmospheric refraction
• Hotter air is optically rarer, cooler air optically denser — light bends as it crosses them.
• A star is a point source very far away, so a small change in its light path is noticeable.
• Planets do not twinkle — they are much nearer, act as extended sources (many point sources), and the flickers average out.
• A star appears slightly higher than its actual position when seen near the horizon.
• Advance sunrise and delayed sunset — the Sun is seen about 2 minutes before actual sunrise and after actual sunset.
• The Sun's disc looks flattened at sunrise and sunset for the same reason.
Do not mix these up
• Refraction vs scattering — twinkling and advance sunrise are refraction; blue sky, red sunset and the Tyndall effect are scattering.
Also asked from this topic: why the Sun's disc looks flattened at sunrise and sunset (atmospheric refraction); the cause of a mirage on a hot road (refraction through hot air layers).

Answer: Option 2 — between the focus and the centre of curvature
With the object between F and C, the image forms beyond C.
It is real, inverted and magnified — the only position that gives all three.
Revision note — Images formed by a concave mirror
• Object at infinity → image at F, real, inverted, highly diminished (point-sized).
• Object beyond C → image between F and C, real, inverted, diminished.
• Object at C → image at C, real, inverted, same size.
• Object between F and C → image beyond C, real, inverted, enlarged.
• Object at F → image at infinity, real, inverted, highly enlarged.
• Object between P and F → image behind the mirror, virtual, erect, enlarged (shaving / dentist's mirror).
Do not mix these up
• Between F and C vs between P and F — both give a magnified image.
• Only F to C gives a real, inverted one; P to F gives a virtual, erect one.
Also asked from this topic: the image when the object is between the pole and focus (virtual and upright); where to place the face in a shaving mirror (between the pole and the focus).

Answer: Option 1 — Pune
In October 2024 Dr Jitendra Singh inaugurated India's first Demonstration Facility for Biopolymers at Jejuri, Pune (Maharashtra), set up by Praj Industries.
Revision note — India's first biopolymer facilities
• Biopolymers are polymers from renewable biological sources (sugarcane, corn); they are biodegradable — an alternative to petroleum plastics.
• The Pune facility makes PLA (polylactic acid), a leading bioplastic.
• It supports the BioE3 policy (Biotechnology for Economy, Environment and Employment), approved by the Union Cabinet in August 2024.
• India's first biopolymer manufacturing plant (PLA) is being set up in Uttar Pradesh by Balrampur Chini Mills at Kumbhi, Lakhimpur Kheri.
• Dr Jitendra Singh is MoS (Independent Charge) for Science and Technology and Earth Sciences, and MoS in the PMO.
Do not mix these up
• Demonstration facility (Pune, Praj, 2024) vs commercial manufacturing plant (Uttar Pradesh, Balrampur Chini).
Also asked from this topic: the state where India's first biopolymer manufacturing plant is being set up (Uttar Pradesh).

Answer: Option 3 — Ashwini Vaishnaw
Union Minister of Information & Broadcasting, Ashwini Vaishnaw, launched the 'Create in India Challenge – Season One' in New Delhi on 22 August 2024.
Revision note — Create in India Challenge and WAVES
• The challenge (25 contests) was launched in the run-up to WAVES — World Audio Visual and Entertainment Summit.
• Aim: build India as a global hub for content creation — animation, gaming, film, music, comics, VFX, AR/VR.
• WAVES 2025 (first edition) was held at Jio World Centre, Mumbai, 1–4 May 2025, inaugurated by PM Narendra Modi.
• Organised by the Ministry of Information & Broadcasting.
• Ashwini Vaishnaw also holds Railways and Electronics & IT.
The same minister holds Railways, I&B and MeitY — a favourite hook in Railway papers.

Answer: Option 2 — New Delhi
The World Sustainable Development Summit (WSDS) 2024 — the 23rd edition — was held in New Delhi on 7–9 February 2024.
It is organised every year by TERI (The Energy and Resources Institute).
Revision note — World Sustainable Development Summit
• Organiser: TERI, New Delhi — TERI's flagship annual event on sustainable development and climate.
• The summit began in 2001 as the Delhi Sustainable Development Summit (DSDS) and was renamed WSDS in 2016.
• WSDS 2024 theme: "Leadership for Sustainable Development and Climate Solutions".
• It is held almost every year in New Delhi.
• The next edition, WSDS 2025 (24th), was held on 5–7 March 2025, again in New Delhi.
Also asked from this topic: the city that hosted WSDS in March 2025 (New Delhi); the edition number of WSDS 2025 (24th); the organiser of WSDS (TERI).
It is TERI's summit, and TERI is in New Delhi — the venue has almost never moved.

Answer: Option 3 — Cuiaba, Brazil
Brazil held the G20 presidency in 2024, so all its ministerial meetings were in Brazil.
The G20 Agriculture Ministers' Meeting was held in September 2024 in the farm state of Mato Grosso, at Cuiabá (Chapada dos Guimarães).
Revision note — G20 in 2023–2024
• G20 = 19 countries + the European Union, and the African Union since 2023; formed in 1999 after the Asian financial crisis.
• India's presidency (2023) — 18th summit at Bharat Mandapam, New Delhi; theme Vasudhaiva Kutumbakam — One Earth, One Family, One Future.
• At New Delhi the African Union became a permanent member.
• Brazil's presidency (2024) — 19th summit at Rio de Janeiro, November 2024; theme Building a Just World and a Sustainable Planet.
• Brazil launched the Global Alliance Against Hunger and Poverty at the Rio summit.
• The presidency passes in a troika: 2023 India → 2024 Brazil → 2025 South Africa (Johannesburg).
Do not mix these up
• Rio de Janeiro hosted the leaders' summit; the agriculture ministers met in Mato Grosso (Cuiabá).
Also asked from this topic: the G20 Summit 2024 venue (Rio de Janeiro); the Rio theme (Building a Just World and a Sustainable Planet); the 2025 Johannesburg theme (Solidarity, Equality, Sustainability).

Answer: Option 1 — 11 March 2024
The Citizenship (Amendment) Act, 2019 came into force only when the Ministry of Home Affairs notified the Citizenship (Amendment) Rules, 2024 on 11 March 2024.
Revision note — Citizenship (Amendment) Act, 2019
• Passed by Parliament in December 2019; it amends the Citizenship Act, 1955.
• Fast-track citizenship for Hindu, Sikh, Buddhist, Jain, Parsi and Christian migrants from Afghanistan, Bangladesh and Pakistan.
• Cut-off date of entry into India: 31 December 2014.
• Residence requirement for naturalisation cut from 11 years to 5 years for these groups.
• Does not apply to Sixth Schedule tribal areas and Inner Line Permit regions of the North-East.
• Citizenship is in the Union List; Articles 5–11 (Part II) of the Constitution deal with citizenship.
Also asked from this topic: the three countries covered by CAA 2019 (Afghanistan, Bangladesh, Pakistan); the areas excluded by the 2024 Rules (Sixth Schedule areas and ILP regions).

Answer: Option 2 — 326
Article 326 says elections to the Lok Sabha and the State Legislative Assemblies are held on the basis of adult suffrage.
Every citizen aged 18 years or more who is not otherwise disqualified can vote.
Revision note — Elections in the Constitution (Part XV)
• Part XV, Articles 324–329, deals with elections.
• Article 324 — the Election Commission: superintendence, direction and control of elections.
• Article 325 — one general electoral roll for each constituency; no one excluded on religion, race, caste or sex.
• Article 326 — adult suffrage; the 61st Amendment Act, 1988 cut the voting age from 21 to 18.
• Article 327 / 328 — Parliament / State Legislature may make laws on elections.
• Article 329 — courts barred from interfering in electoral matters.
Do not mix these up
• Article 352 vs 326 — 352 is National Emergency; 340 is the Backward Classes Commission; 318 is about Public Service Commission members.
Also asked from this topic: the amendment that lowered the voting age from 21 to 18 (61st Amendment, 1988); the minimum voting age for State Legislative Assembly elections (18 years).

Answer: Option 4 — 7^(th) Constitutional Amendment Act, 1956
The 7th Amendment Act, 1956 inserted Article 350B, creating a Special Officer for Linguistic Minorities.
He is known as the Commissioner for Linguistic Minorities and reports to the President.
Revision note — Linguistic minorities and the 7th Amendment
• Article 350B is in Part XVII (Official Language); the officer is appointed by the President.
• His reports are laid before each House of Parliament and sent to the state governments concerned.
• The office was set up in 1957; it now works under the Ministry of Minority Affairs.
• The same 7th Amendment (1956) also inserted Article 350A — instruction in the mother tongue at the primary stage.
• The 7th Amendment reorganised states on linguistic lines (States Reorganisation Act, 1956): abolished Part A, B, C, D states and created 14 states and 6 Union Territories.
• Article 29 protects the culture, language and script of any section of citizens; Article 30 lets minorities set up educational institutions.
Also asked from this topic: the Article that created the Special Officer for Linguistic Minorities (Article 350B); the Article giving minorities the right to establish educational institutions (Article 30).
350A and 350B arrived together with state reorganisation in 1956 — link all three to the 7th Amendment.

Answer: Option 2 — Equilibrium is the situation where there is no tendency for any change.
At equilibrium all the opposing influences balance exactly, so the state does not tend to change on its own.
Revision note — Equilibrium in economics and science
• Market (economics): equilibrium price is where quantity demanded = quantity supplied; no buyer or seller wants to change their plan.
• Mechanical: net force and net torque on a body are zero — it stays at rest or in uniform motion.
• Chemical: rate of forward reaction = rate of backward reaction; concentrations stay constant. It is dynamic, not static.
• Thermal: two bodies in contact at the same temperature — no net heat flow (basis of the zeroth law).
• Le Chatelier's principle: a disturbed equilibrium shifts to oppose the change.
• Stable, unstable, neutral equilibrium — a body returns, moves away, or stays in a new position when slightly displaced.
• In economics, market equilibrium is where demand = supply — again, no tendency for the price to change.
Do not mix these up
• Dynamic vs static — chemical equilibrium looks still, but both reactions keep running at equal rates.
Also asked from this topic: the effect of adding a product at equilibrium (shifts left, Le Chatelier); the temperature at which ice, water and vapour coexist in equilibrium (0.01°C).

Answer: Option 4 — A hall for prayer and assembly
A chaitya is a Buddhist prayer hall where monks and devotees gathered; it usually has a small stupa at the far, rounded (apsidal) end.
Revision note — Buddhist architecture
• Stupa: a hemispherical mound over relics of the Buddha; parts — anda (dome), harmika (railing on top), yashti and chhatra, toranas (gateways).
• Chaitya: prayer / congregational hall; famous rock-cut chaityas at Karle (largest), Bhaja, Ajanta Caves 9, 10, 19, 26.
• Vihara: monastery — residence of monks, with cells around a central hall.
• Sanchi Stupa (Madhya Pradesh) was begun by Ashoka; its toranas show Jataka stories.
• Bharhut reliefs (2nd century BCE) → Sanchi gateways → Mathura school — the development of Buddhist sculpture.
• In early art the Buddha is shown only by symbols — empty seat, footprints, stupa, wheel, bodhi tree.
Do not mix these up
• Chaitya vs vihara — chaitya is for prayer; vihara is for living.
Also asked from this topic: the main function of chaityas (congregational halls); what the Sanchi toranas depict (Jataka stories); the stupa part that is the abode of the gods (harmika).

Answer: Option 4 — 2021
'Indian Culture: A Compendium of Indian History, Culture and Heritage' was published in 2021.
It is the English translation of historian Dr S. Srikanta Sastri's Kannada work 'Bharatiya Samskriti' (1954).
Revision note — The book and its author
• Translated into English by Prof. S. Naganath, the author's son.
• Published by Notion Press in 2021.
• S. Srikanta Sastri (1904–1974) was a historian and Indologist from Mysore, Karnataka.
• The original Kannada book 'Bharatiya Samskriti' came out in 1954.
• It surveys Indian history, religion, art, literature and heritage from ancient times.
Year-of-publication questions often turn on translation — the English edition's date, not the original's, is asked.

Answer: Option 4 — Haryana
The 61st National (Senior) Chess Championship, 2024, run by the All India Chess Federation (AICF), was held at Gurugram, Haryana.
Revision note — Indian chess
• All India Chess Federation (AICF) runs national chess; FIDE (founded 1924, Paris) runs world chess from Lausanne.
• Viswanathan Anand became India's first Grandmaster in 1988 and won the World Championship five times.
• India won both gold medals (open and women) at the 45th Chess Olympiad, Budapest, September 2024.
• D. Gukesh became the youngest undisputed World Champion (December 2024, Singapore, beating Ding Liren).
• India hosted the 44th Chess Olympiad at Mamallapuram (Chennai) in 2022; mascot Thambi.
Also asked from this topic: India's first chess Grandmaster (Viswanathan Anand); the full form of FIDE (Federation Internationale des Echecs).

Answer: Option 1 — 78
Gandhi set out on the Salt March with 78 trusted volunteers of the Sabarmati Ashram.
It began on 12 March 1930 and reached Dandi on 6 April 1930.
Revision note — Dandi March and Civil Disobedience (1930)
• Route: Sabarmati Ashram (Ahmedabad) → Dandi (coastal Gujarat), about 240 miles (385 km) in 24 days.
• At Dandi Gandhi made salt from sea water and broke the salt law — the start of the Civil Disobedience Movement.
• The salt tax and the British monopoly on salt were chosen because they hit every Indian.
• C. Rajagopalachari led a parallel salt march from Tiruchirappalli to Vedaranyam (Madras Presidency).
• The movement was suspended by the Gandhi–Irwin Pact (1931) and relaunched in 1932 after the Second Round Table Conference.
Also asked from this topic: the year Gandhi broke the Salt Act at Dandi (1930); the salt-march leader in Madras Presidency (C. Rajagopalachari); the movement relaunched in 1932 (Civil Disobedience).

Answer: Option 3 — Around 20°N-25°N
In July the ITCZ moves north with the overhead sun and settles over the Gangetic plain at about 20°N–25°N.
Here it is called the monsoon trough.
Revision note — ITCZ and the Indian monsoon
• ITCZ = the low-pressure belt where the north-east and south-east trade winds converge.
• It normally lies near the equator (the doldrums) and shifts with the apparent movement of the sun.
• Summer: intense heating of north-west India deepens the low; the ITCZ pulls in the south-east trades, which cross the equator and turn into the south-west monsoon.
• Winter: the ITCZ shifts south; its southward retreat marks the withdrawal of the monsoon.
• A break in the monsoon occurs when the monsoon trough moves away from its normal position.
Also asked from this topic: the zone near the equator where the trade winds of both hemispheres meet (ITCZ); the change that marks the withdrawal of the monsoon (southward shift of the ITCZ).

Answer: Option 4 — Jawaharlal Nehru Port
Jawaharlal Nehru Port (JNPA) at Nhava Sheva, Navi Mumbai is the first major port of India whose berths are all run by private operators under PPP.
The port authority now acts only as a landlord — it owns the land and water, private firms run the terminals.
Revision note — Major ports of India
• Major ports are under the Union Ministry of Ports, Shipping and Waterways; there are 12 of them, run under the Major Port Authorities Act, 2021.
• JNPA was commissioned on 26 May 1989 and is India's largest container port among the major ports.
• JNPA with Maharashtra Maritime Board is building the deep-draft Vadhavan port in Palghar, Maharashtra (foundation stone August 2024).
• West coast major ports north to south: Deendayal (Kandla), Mumbai, JNPA, Mormugao, New Mangalore, Cochin.
• East coast: V.O. Chidambaranar (Tuticorin), Chennai, Kamarajar (Ennore), Visakhapatnam, Paradip, Syama Prasad Mookerjee (Kolkata).
Do not mix these up
• Mundra (Gujarat) is a large private port of the Adani group, not a major port.
• Kamarajar Port (Ennore) was the first major port set up as a company; JNPA is the first fully PPP-operated major port.
Also asked from this topic: the southernmost of Kandla, JNPA, Mormugao and New Mangalore (New Mangalore); the west-coast port among Cochin, Chennai, Paradip and Visakhapatnam (Cochin).

Answer: Option 4 — The Cholas
The tripartite struggle for Kannauj was fought only by the Gurjara-Pratiharas, the Palas and the Rashtrakutas.
The Cholas ruled far south in the Kaveri delta and took no part in it.
Revision note — The tripartite struggle for Kannauj
• Fought for about 200 years (8th–10th century CE) for control of Kannauj (Kanyakubja) and the Ganga valley.
• Kannauj was the prize because it had been Harshavardhana's capital — the symbol of power over north India.
• Gurjara-Pratiharas — western India (Rajasthan, Gujarat); Palas — Bengal and Bihar; Rashtrakutas — the Deccan (capital Manyakheta).
• Leading kings: Dharmapala and Devapala (Pala), Nagabhata II and Mihira Bhoja (Pratihara), Dhruva and Govinda III (Rashtrakuta).
• The Pratiharas finally held Kannauj — Nagabhata II captured it and made it their capital.
• The long war weakened all three and opened the way for later Rajput states and Mahmud of Ghazni's raids.
Do not mix these up
• Cholas — imperial line founded by Vijayalaya (c. 850 CE) at Thanjavur; their great rivals were the Rashtrakutas and Chalukyas, not in Kannauj.
Also asked from this topic: the dynasty that ruled Kannauj during the struggle (Gurjara-Pratiharas); the name of this conflict (tripartite struggle); the founder of the Rashtrakuta dynasty (Dantidurga).