Chemical Bonding – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Chemical Bonding with detailed solutions and explanations.

Chapter-wise PYQs • Concept-based explanations • Exam insights

NDA 2026-II

Q. 1. Consider the following statements regarding hydrogen bonds :

I. Hydrogen bonds can only form when hydrogen is bonded to oxygen, nitrogen or fluorine.

II. Hydrogen bonds are intramolecular only.

III. The strength of a hydrogen bond decreases with a decrease in the electronegativity of the two bonded atoms.

Which of the statements given above is/are not correct ?

(a) I only

(b) II only

(d) II and III

Answer: (b) II only

Explanation: Statement I is correct: hydrogen bonds form when H is bonded to highly electronegative atoms – O, N, or F. Statement II is NOT correct: hydrogen bonds can be both intramolecular (within the same molecule, e.g. in o-nitrophenol) and intermolecular (between different molecules, e.g. in water). Statement III is correct: stronger H-bonds form when electronegativity of the bonded atoms is higher. So only Statement II is not correct. Concept Tested: Properties of hydrogen bonds – intramolecular and intermolecular

Q. 2. Ionic compounds have high melting and boiling points. This is due to :

(a) the presence of strong electrostatic forces between ions in the crystal lattice.

(b) the weak intermolecular van der Waals forces.

(d) lower lattice energy.

Answer: (a) the presence of strong electrostatic forces between ions in the crystal lattice.

Explanation: Ionic compounds have high melting and boiling points because the ions are held together by strong electrostatic attractions (ionic bonds) in a crystalline lattice. A large amount of energy is needed to break these forces. Van der Waals forces are weak – associated with covalent molecules. A sea of delocalized electrons is a property of metals. Concept Tested: Properties of ionic compounds – high melting points due to lattice energy

NDA 2024-I

Q. 3. What is the coordination number of Na⁺ and Cl⁻ ions in NaCl lattice?

(a) 6, 1

(b) 1, 6

(d) 5, 5

Answer: (c) 6, 6

Explanation: In the NaCl crystal lattice, each Na⁺ ion is surrounded by 6 Cl⁻ ions, and each Cl⁻ ion is surrounded by 6 Na⁺ ions. The coordination number of both Na⁺ and Cl⁻ is 6. Concept Tested: NaCl crystal structure – coordination number

NDA 2022-I

Q. 4. Which one of the following is a covalent compound?

(a) Calcium oxide

(b) Sodium nitride

(d) Zinc sulphide

Answer: (c) Silicon carbide

Explanation: Silicon carbide (SiC) is a covalent compound – silicon and carbon are both non-metals that form covalent bonds. Calcium oxide (CaO) and zinc sulphide (ZnS) are ionic compounds. Sodium nitride (Na₃N) is also ionic. SiC has a covalent network structure similar to diamond. Concept Tested: Identifying covalent compounds – silicon carbide

NDA 2021-II

Q. 5. What is the total number of covalent bonds in methanol?

(a) 3

(b) 4

(d) 6

Answer: Editorial Review Required

Explanation: Methanol CH₃OH has: 3 C-H bonds + 1 C-O bond + 1 O-H bond = 5 covalent bonds. However, if the question counts only bonds to carbon (excluding O-H): 3+1=4. The intended answer appears to be (b) 4, counting bonds to C only. Note: If all bonds are counted including O-H, the answer would be 5. Verify against official NDA 2021-II key. Concept Tested: Covalent bond counting in methanol

NDA 2020

Q. 6. How many covalent bonds are present in a Chloropropane molecule having molecular formula C₃H₇Cl?

(a) 6

(b) 8

(d) 10

Answer: (d) 10

Explanation: Chloropropane C₃H₇Cl: count all bonds. Structure: CH₃-CH₂-CH₂Cl. C-C bonds: 2. C-H bonds: 3+2+2 = 7. C-Cl bond: 1. Total = 2+7+1 = 10 covalent bonds. Concept Tested: Counting covalent bonds in an organic molecule

NDA 2019-I

Q. 7. Which one of the following energy is stored in the links between the atoms?

(a) Nuclear energy

(b) Chemical energy

(d) Thermal energy

Answer: (b) Chemical energy

Explanation: Chemical energy is the energy stored in chemical bonds between atoms. When bonds are broken or formed during a chemical reaction, this energy is released or absorbed. Nuclear energy is stored in the nucleus. Potential and thermal energy have different definitions. Concept Tested: Chemical energy – energy stored in chemical bonds

NDA 2018-II

Q. 8. The atomic number of an element is 8. How many electrons will it gain to form a compound with sodium?

(a) One

(b) Two

(d) Four

Answer: (b) Two

Explanation: Atomic number 8 is oxygen (O), with electronic configuration 2,6. It has 6 valence electrons and needs 2 more to complete the octet. Sodium (Na) has 1 valence electron and loses it. To form Na₂O, oxygen gains 2 electrons (forming O²⁻) and pairs with two Na⁺ ions. Concept Tested: Electron gain to achieve octet – oxygen in ionic bonding

NDA 2016-II

Q. 9. Which one of the following statements is correct?

(a) Covalent bonds are directional

(b) Ionic bonds are directional

(d) Both covalent and ionic bonds are non-directional

Answer: (a) Covalent bonds are directional

Explanation: Covalent bonds have a definite direction in space (determined by orbital overlap geometry) – they are directional. Ionic bonds arise from electrostatic attraction between oppositely charged ions, which acts in all directions – ionic bonds are non-directional. So only (a) is correct. Concept Tested: Directionality of covalent vs ionic bonds

NDA 2014-II

Q. 10. Which of the following element combinations will form ionic compounds?

1. Ca (Z = 20) and Ti (Z = 22)

2. Si (Z = 14) and Br (Z = 35)

3. Mg (Z = 12) and Cl (Z = 17)

Select the correct answer using the code given below.

(a) 2 only

(b) 3 only

(d) 1, 2 and 3

Answer: (b) 3 only

Explanation: Ionic compounds form between a metal (especially from Groups 1 and 2) and a non-metal. Mg (metal, Group 2) + Cl (non-metal, Group 17) → MgCl₂ – ionic. Ca (Group 2 metal) + Ti (transition metal, Z=22) → both metals, no ionic compound formed. Si (metalloid) + Br (non-metal) → likely covalent (SiBr₄). Only combination 3 forms an ionic compound. Concept Tested: Conditions for ionic bond formation – metal + non-metal

NDA 2013-I

Q. 11. The bond which is present between water molecules is

(a) electrovalent bond

(b) covalent bond

(d) van der Waals bond

Answer: (c) hydrogen bond

Explanation: The bond between water molecules (intermolecular) is the hydrogen bond. Within each water molecule (intramolecular) are covalent bonds between O and H. But the question asks about the bond between water molecules, which is the hydrogen bond formed between the O of one molecule and the H of another. Concept Tested: Hydrogen bonding in water – intermolecular forces

★ JOVIK Exam Insight: A common NDA trap: covalent bonds exist within a water molecule; hydrogen bonds exist between water molecules. This distinction is tested frequently.