Chemical Bonding – NDA Chemistry PYQs

Q1. What are the types of bonds present in CuSO₄·5H₂O?
(a) Electrovalent and covalent
(b) Electrovalent and coordinate covalent
(c) Electrovalent, covalent, coordinate covalent and hydrogen bonds
(d) Covalent and coordinate covalent

Answer: (c) Electrovalent, covalent, coordinate covalent and hydrogen bonds
CuSO₄·5H₂O contains all four bond types. Cu²⁺ and SO₄²⁻ are held by ionic (electrovalent) bonds. S and O inside sulphate are held by covalent bonds. Cu²⁺ and 4 water molecules are held by coordinate bonds (water donates lone pairs to Cu²⁺). The 5th water molecule is held to the rest by hydrogen bonds.
[NDA 2006-II]

---

Q2. The octet rule is not valid for which one of the following molecules?
(a) CO₂ (b) H₂S (c) NH₃ (d) BF₃

Answer: (d) BF₃
In BF₃, boron forms 3 bonds with 3 fluorine atoms. This gives boron only 6 electrons around it — not 8. The octet is incomplete. Boron is an exception to the octet rule. CO₂, H₂S, and NH₃ all satisfy the octet rule.
[NDA 2007-I]

---

Q3. The bond which is present between water molecules is:
(a) Electrovalent bond (b) Covalent bond (c) Hydrogen bond (d) Van der Waals bond

Answer: (c) Hydrogen bond
Inside a single water molecule, the O–H bonds are covalent. But the force between two different water molecules is a hydrogen bond. Oxygen (highly electronegative) makes the hydrogen slightly positive. This δ+ hydrogen is attracted to the lone pair on oxygen of a neighbouring water molecule.
[NDA 2013-I]

---

Q4. Statement I: Water is a high boiling point liquid.
Statement II: Hydrogen bonding in water is responsible for the high boiling point of water.
(a) Both true, II correctly explains I
(b) Both true, II does not explain I
(c) I true, II false
(d) I false, II true

Answer: (a) Both true, Statement II correctly explains Statement I
Water boils at 100°C — very high for a molecule with molecular mass of only 18 u. This is because water molecules are held together by strong hydrogen bonds. Extra energy is needed to break these bonds. So water needs more heat to boil than expected.
[NDA 2012-I]

Q5. Which one of the following is a covalent compound?
(a) Calcium oxide (b) Sodium nitride (c) Silicon carbide (d) Zinc sulphide

Answer: (c) Silicon carbide
Silicon carbide (SiC) is formed between two non-metals (silicon and carbon). Non-metal + non-metal = covalent bond. Calcium oxide (CaO) = metal + non-metal = ionic. Sodium nitride (Na₃N) = metal + non-metal = ionic. Zinc sulphide (ZnS) = metal + non-metal = ionic.
[NDA 2022-I]

---

Q6. Which one of the following is correct?
(a) Covalent bonds are directional
(b) Ionic bonds are directional
(c) Both covalent and ionic bonds are directional
(d) Both covalent and ionic bonds are non-directional

Answer: (a) Covalent bonds are directional
Covalent bonds form by electron sharing along a specific axis — they have a definite direction in space. This is why covalent molecules have specific shapes. Ionic bonds are non-directional — the electrostatic attraction between ions acts equally in all directions.
[NDA 2016-II]

---

Q7. What is the total number of covalent bonds in methanol?
(a) 3 (b) 4 (c) 5 (d) 6

Answer: (c) 5
Methanol is CH₃OH. Count all bonds: 3 C–H bonds + 1 C–O bond + 1 O–H bond = 5 covalent bonds. Draw the structure to count clearly.
[NDA 2021-II]

---

Q8. How many covalent bonds are present in a chloropropane molecule having molecular formula C₃H₇Cl?
(a) 6 (b) 8 (c) 9 (d) 10

Answer: (d) 10
C₃H₇Cl: 2 C–C bonds + 7 C–H bonds + 1 C–Cl bond = 10 covalent bonds. Count each bond in the structural formula carefully.
[NDA 2020]

Q9. The number of valence electrons in the O²⁻ ion is:
(a) 4 (b) 6 (c) 8 (d) 10

Answer: (c) 8
Oxygen normally has 6 valence electrons (configuration 2,6). The O²⁻ ion has gained 2 extra electrons. So it now has 6 + 2 = 8 valence electrons. Its outer shell is now full — like the noble gas neon.
[NDA 2014-I]

---

Q10. 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)
   (a) 1 only (b) 3 only (c) 2 and 3 (d) 1 and 3

Answer: (b) 3 only
Mg is a metal and Cl is a non-metal → metal + non-metal → ionic bond → MgCl₂.
Ca (metal) and Ti (metal) → two metals → metallic bond, not ionic.
Si (metalloid/non-metal) and Br (non-metal) → two non-metals → covalent bond, not ionic.
[NDA 2014-II]

---

Q11. Which one of the following statements is NOT correct about micelles?
(a) The oil and dirt gets collected in the centre of the micelle
(b) Soap micelles scatter light
(c) Soaps are ammonium salts of long chain carboxylic acids
(d) Soap forms insoluble precipitates with calcium and magnesium ions in hard water

Answer: (c) Soaps are ammonium salts of long chain carboxylic acids
Soaps are sodium or potassium salts — NOT ammonium salts — of long chain fatty acids. Options (a), (b), and (d) are all correct. Oil collects in the micelle centre, soap micelles scatter light (Tyndall effect), and soap does form insoluble scum with hard water ions.
[NDA 2021-I]

Q12. Which one of the following statements is NOT correct about micelles?
(a) The molecules of soap are sodium or potassium salts of long chain fatty acids
(b) The molecules of soap contain both hydrophobic and hydrophilic ends
(c) Detergents are more effective than soaps in hard water
(d) In micelles the ionic-end of the molecules is towards the oil droplet while the other end faces outside

Answer: (d) In micelles the ionic-end of the molecules is towards the oil droplet
This is false. In a micelle, the hydrophobic (non-polar) tail points inward towards the oil. The ionic (hydrophilic) head points outward towards the water. Statement (d) says the opposite — it is the false statement.
[NDA 2025-I]

---

Q13. The cleaning action of soap and detergent in water is due to the formation of:
(a) Micelle (b) Salt (c) Base (d) Acid

Answer: (a) Micelle
Soap molecules surround oil droplets — their hydrophobic tails face the oil and hydrophilic heads face the water. This spherical structure is called a micelle. The micelle keeps the oil suspended in water so it can be washed away.
[NDA 2015-I]

---

Q14. Soap with water forms:
(a) Metallotropic liquid crystal
(b) Thermotropic liquid crystal
(c) Homogeneous solution
(d) Lyotropic liquid crystal

Answer: (d) Lyotropic liquid crystal
When soap dissolves in water above a certain concentration, soap molecules self-organise into micelles. This organised structure in a solvent is called a lyotropic liquid crystal. Order is induced by concentration — not by temperature.
[NDA 2024-I]

Q15. Emulsion is known as a:
(a) Colloidal solution of substances having different physical states
(b) True solution
(c) Distillation mixture for making alcohols
(d) Colloidal solution of two liquids

Answer: (d) Colloidal solution of two liquids
An emulsion is a colloidal dispersion of one liquid in another immiscible liquid. Both components are liquids. Examples: milk (fat droplets in water), butter (water droplets in fat), and mayonnaise.
[NDA 2016-II]

---

Q16. Water is a good solvent. Which of the following statements about water as a solvent is correct?

1. Water is a good solvent for ionic compounds but poor solvent for covalent compounds
2. Water is a good solvent for covalent compounds but poor solvent for ionic compounds
3. Water has maximum density at the temperature 277 K

(a) 1 and 3 only (b) 2 and 3 only (c) 1 only (d) 1, 2 and 3

Answer: (a) 1 and 3 only
Statement 1 is correct — water is polar, so it dissolves ionic compounds well (like dissolves like). Statement 3 is correct — water has maximum density at 4°C = 277 K. Statement 2 is false — water is a poor solvent for non-polar covalent compounds like oils and fats.
[NDA 2010-II]

Q18. Which one of the following substances is most likely to be used as soap?
(a) CH₃(CH₂)₁₂COOCH₃
(b) CH₃(CH₂)₅O(CH₂)₅CH₃
(c) CH₃(CH₂)₁₂COONa
(d) CH₃(CH₂)₁₂CHCl₂

Answer: (c) CH₃(CH₂)₁₂COONa
Soap is the sodium salt of a long chain fatty acid. Option (c) has the –COONa group (sodium carboxylate) attached to a long carbon chain. That is exactly the structure of soap. Option (a) is an ester, (b) is an ether, and (d) is a chlorinated compound — none of these are soaps.
[NDA 2014-II]