Chemical Bonding PYQs – Chemistry, SSC & Railway

Explanation:
Statement I is correct: a covalent bond forms by the mutual sharing of electron pairs between atoms. Statement II is incorrect: covalent bonding typically occurs between two non-metal atoms (both wanting to gain/share electrons), not between a metal and a non-metal — that combination typically forms an ionic bond via electron transfer.
Correct Answer: Option 2 – Only statement I is correct

Statement 1 says metals and non-metals react by sharing electrons.
This is incorrect because metals and non-metals typically react by transferring electrons, forming ionic bonds, not by sharing electrons.
Statement 2 says the bond formed between them is covalent.
This is false since the bond between metals and non-metals is ionic, not covalent.
Therefore, Statement 1 is false and Statement 2 is false is not correct.
Only Statement 1 is false and Statement 2 is false, but option 1 says Statement 1 is true and Statement 2 is false, so let's verify carefully.
Metals and non-metals generally form ionic bonds by electron transfer.
Hence Statement 1 is false.
Statement 2 claiming the bond is covalent is false.
Thus, both statements are false.
The correct option is Option 3.
Final answer: Option 1

The reaction between sodium and chlorine forms sodium chloride (NaCl).
Sodium (Na) loses one electron to achieve a stable electron configuration.
Chlorine (Cl) gains one electron to complete its outer shell.
This transfer creates Na+ and Cl- ions.
These oppositely charged ions attract each other due to strong electrostatic forces, forming an ionic bond.
This ionic bond gives the compound high stability.
Hence, sodium chloride is stable because of ionic bonding, not sharing of electrons or metallic bonding.
Final answer: Option 3

Magnesium forms Mg2+ ions by losing two electrons, not Mg3+ ions.
The compound magnesium oxide contains ionic bonds.
Oxygen gains two electrons to form O2- ions.
Therefore, the incorrect statement is that magnesium forms Mg3+ ions.
Final answer: Option 2

Correct Answer: Option 2 — CH₄
A covalent compound is formed when two atoms share electrons instead of transferring them. Sharing happens between two non-metals, because neither of them can easily give its electrons away.
Methane, CH₄, is the textbook example. Carbon has 4 valence electrons and needs 4 more to complete its octet; instead of losing or gaining 4 electrons (which would need far too much energy), it shares one electron with each of four hydrogen atoms, forming four single covalent bonds. Both carbon and hydrogen are non-metals, so CH₄ is covalent.
An ionic compound, by contrast, forms between a metal and a non-metal by complete transfer of electrons. Simply look for a metal in the formula: if there is one, the compound is almost always ionic.
❌ Why the other options are incorrect
✗ MgO — ionic; magnesium (a metal) gives away 2 electrons to oxygen, producing Mg²⁺ and O²⁻.
✗ MgCl₂ — ionic; magnesium transfers one electron to each of two chlorine atoms, giving Mg²⁺ and 2Cl⁻.
✗ NaCl — the classic ionic compound; sodium loses one electron to chlorine to form Na⁺ and Cl⁻, held together by strong electrostatic force.
📌 SSC & Railway Exam Facts
• Metal + non-metal → ionic bond (transfer); non-metal + non-metal → covalent bond (sharing).
• Covalent compounds have low melting and boiling points, are poor conductors and are generally insoluble in water but soluble in organic solvents.
• Ionic compounds are hard crystalline solids with high melting points, soluble in water, and conduct electricity in molten or aqueous state (not when solid).
• Bond types: single bond (H₂, CH₄, Cl₂), double bond (O₂, C₂H₄, CO₂), triple bond (N₂, C₂H₂).
• Methane (CH₄) is the first member of the alkane series and the main constituent of CNG, biogas and natural gas; it is also a greenhouse gas (marsh gas).

Correct Answer: Option 4 — In an ionic compound, the transfer of electrons takes place from a metal to a non-metal.
An ionic (electrovalent) compound is formed by the complete transfer of electrons from one atom to another. Metals have few valence electrons and low ionisation energy, so they lose electrons easily and become cations. Non-metals have nearly complete outer shells and high electron affinity, so they gain those electrons and become anions.
⚗️ The Reaction
Na → Na⁺ + e⁻ and Cl + e⁻ → Cl⁻, giving Na⁺Cl⁻
• Sodium (2, 8, 1) loses its single valence electron to attain the stable configuration of neon.
• Chlorine (2, 8, 7) gains that electron to attain the stable configuration of argon.
• The oppositely charged ions are held by a strong electrostatic force of attraction — the ionic bond.
❌ Why the other options are incorrect
✗ from a metal to a metal — two metals both want to lose electrons; neither will accept them, so they form an alloy or metallic bond, not an ionic bond.
✗ from a non-metal to a non-metal — two non-metals both want to gain electrons, so they share electrons instead and form a covalent bond (H₂O, CO₂, CH₄).
✗ from a non-metal to a metal — this reverses the actual direction; a non-metal is electronegative and does not donate electrons to a metal.
📌 SSC & Railway Exam Facts
• Metal loses e⁻ → cation (+); non-metal gains e⁻ → anion (−); e.g. NaCl, MgCl₂, CaO, MgO.
• Ionic compounds have high melting and boiling points and are usually solid and brittle.
• They conduct electricity in molten or aqueous state, but not in solid state.
• They are generally soluble in water and insoluble in kerosene or petrol.
• Ionic bond = transfer of electrons; covalent bond = sharing of electrons.

Correct Answer: Option 1 — Na ions are positively charged, and Cl ions are negatively charged
Sodium chloride (NaCl) is a typical ionic compound formed by the transfer of one electron from the metal to the non-metal.
• Sodium (Na), atomic number 11, has the configuration 2, 8, 1. It loses its single outermost electron to attain the stable octet of neon, becoming Na⁺ — a cation with 11 protons but only 10 electrons, hence positively charged.
• Chlorine (Cl), atomic number 17, has the configuration 2, 8, 7. It gains one electron to complete its octet, becoming Cl⁻ — an anion with 17 protons but 18 electrons, hence negatively charged.
The strong electrostatic attraction between Na⁺ and Cl⁻ builds the crystal lattice of common salt. Remember: a metal loses electrons and forms a cation; a non-metal gains electrons and forms an anion.
❌ Why the other options are incorrect
✗ Ions of both Na and Cl are negatively charged — impossible; two like charges would repel, and a compound must be electrically neutral overall.
✗ Cl ions are positively charged, and Na ions are negatively charged — this reverses the roles; a metal can never gain electrons to become negative here.
✗ Ions of both Na and Cl are positively charged — again impossible; there must be one cation and one anion to form an ionic bond.
📌 SSC & Railway Exam Facts
• Cation = positive (loses electrons, e.g. Na⁺, Mg²⁺, Ca²⁺); anion = negative (gains electrons, e.g. Cl⁻, O²⁻, SO₄²⁻).
• In electrolysis, cations move to the cathode and anions to the anode.
• Na: 2,8,1 and Cl: 2,8,7; after transfer both attain the noble gas configuration.
• NaCl = common salt, used to make NaOH (chlor-alkali process), washing soda, baking soda, bleaching powder.
• Ionic compounds conduct electricity in molten or aqueous state, not as solids.

Correct Answer: Option 4 — H₂
A covalent bond is formed by the mutual sharing of electrons between two atoms. Sharing one pair gives a single bond, two pairs a double bond and three pairs a triple bond.
A hydrogen atom has only 1 electron and needs 1 more to reach the stable duplet of helium. So two hydrogen atoms share one electron pair each way — exactly one shared pair — giving the molecule H–H, a single covalent bond.
Bond strength increases from single to triple, while bond length decreases; that is why N₂ (triple bond) is very unreactive.
❌ Why the other options are incorrect
✗ CO₂ — carbon shares two pairs with each oxygen, giving O=C=O, that is two double bonds (four shared pairs in all).
✗ N₂ — each nitrogen needs 3 electrons, so the two atoms share three pairs, giving a triple bond (N≡N), the strongest of the three.
✗ O₂ — each oxygen needs 2 electrons, so they share two pairs, giving a double bond (O=O).
📌 SSC & Railway Exam Facts
• Single bond = 1 shared pair, double = 2 pairs, triple = 3 pairs.
• H₂, Cl₂, HCl, CH₄, H₂O and NH₃ contain only single covalent bonds.
• Covalent compounds have low melting and boiling points, are poor conductors and are mostly insoluble in water.
• Ionic bond = transfer of electrons (NaCl); covalent bond = sharing of electrons (H₂O).
• Carbon forms four covalent bonds — this tetravalency plus catenation explains the huge number of carbon compounds.