1. The total number of orbitals present in the fourth shell (n = 4) is:

  • A. 8
  • B. 16
  • C. 18
  • D. 32

Answer: B. 16

Explanation: The number of orbitals in the nth shell is n². For n = 4, the number of orbitals = 4² = 16.

2. Which of the following has the smallest ionic radius?

  • A. O2−
  • B. F−
  • C. Na+
  • D. Mg2+

Answer: D. Mg2+

Explanation: All four ions are isoelectronic (10 electrons). In an isoelectronic series, ionic radius decreases with increasing nuclear charge. Mg²⁺ has the highest nuclear charge.

3. Which law states that at constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure?

  • A. Charles' law
  • B. Avogadro's law
  • C. Boyle's law
  • D. Gay-Lussac's law

Answer: C. Boyle's law

Explanation: Boyle's law states that P × V = constant for a fixed mass of gas at constant temperature.

4. Which of the following molecules has a linear geometry?

  • A. NH3
  • B. H2O
  • C. CO2
  • D. SO2

Answer: C. CO2

Explanation: Carbon dioxide has two bonding regions around the central carbon atom and no lone pairs, giving a linear geometry with a bond angle of 180°.

5. Which of the following compounds contains the peroxide ion (O22−)?

  • A. Na2O
  • B. H2O
  • C. Na2O2
  • D. KO2

Answer: C. Na2O2

Explanation: Sodium peroxide (Na₂O₂) contains the peroxide ion (O₂²⁻), whereas KO₂ contains the superoxide ion (O₂⁻).

6. Which of the following is an example of a disproportionation reaction?

  • A. Zn + CuSO4 → ZnSO4 + Cu
  • B. 2H2O2 → 2H2O + O2
  • C. AgNO3 + NaCl → AgCl + NaNO3
  • D. CaCO3 → CaO + CO2

Answer: B. 2H2O2 → 2H2O + O2

Explanation: In hydrogen peroxide, oxygen has an oxidation state of –1. It is simultaneously oxidized to 0 and reduced to –2.

7. Which functional group is present in carboxylic acids?

  • A. –CHO
  • B. –COOH
  • C. –OH
  • D. –NH2

Answer: B. –COOH

Explanation: Carboxylic acids contain the carboxyl functional group (–COOH), which imparts acidic properties.

8. Which transition metal ion imparts a deep blue colour to aqueous copper sulfate solution?

  • A. Cu+
  • B. Cu2+
  • C. Fe2+
  • D. Zn2+

Answer: B. Cu2+

Explanation: Hydrated Cu²⁺ ions ([Cu(H₂O)₆]²⁺) are responsible for the characteristic blue colour of copper sulfate solution.

9. Which of the following compounds undergoes nucleophilic substitution most readily?

  • A. CH3Cl
  • B. C2H5Cl
  • C. (CH3)3CCl
  • D. C6H5Cl

Answer: C. (CH3)3CCl

Explanation: Tert-butyl chloride readily undergoes SN1 substitution because it forms a highly stable tertiary carbocation.

10. Which of the following compounds will produce iodoform with I2/NaOH?

  • A. Methanal
  • B. Benzaldehyde
  • C. Ethanol
  • D. Formic acid

Answer: C. Ethanol

Explanation: Ethanol is oxidized to acetaldehyde, which contains the CH₃CO– group required for a positive iodoform test.