12th Chapter Solved Exercise MCQs of FSC Second Year Chemistry

The 12th Chapter Solved Exercise MCQs of FSC 2nd-year Chemistry provides a complete set of solved multiple-choice questions (MCQs). Each MCQ comes with a brief explanation to help you understand the correct answer. These solutions are designed to support students in preparing for their exams, making complex concepts easier to grasp and ensuring a solid foundation for success.

12th chapter solved MCQs with explanation

1. The carbon atom of a carbonyl group is:
(a) sp hybridized
(b) sp² hybridized
(c) sp³ hybridized
(d) none of these

Explanation: Option (b) is correct. Because carbon atom in a carbonyl group (C=O) forms three bonds: one double bond with oxygen (which includes one sigma and one pi bond) and one single bond with another group. Sp² hybridization involves three orbitals that form sigma bonds and a separate p orbital for the pi bond.

2. Formalin is:
(a) 10% solution of formaldehyde in water
(b) 20% solution of formaldehyde in water
(c) 40% solution of formaldehyde in water
(d) 60% solution of formaldehyde in water

Explanation: Option (a) is correct. Because Formalin is a common aqueous solution of formaldehyde gas. It typically contains about 37-40% formaldehyde by weight, but it is usually diluted to a 10% solution for practical use. This concentration makes it suitable for preserving biological specimens and other applications.

3. Which of the following will have the highest boiling point?
(a) Methanal
(b) Ethanal
(c) Propanal
(d) 2-Hexanone

Explanation: Option (b) is correct. Because

4. Ketones are prepared by the oxidation of:
(a) Primary alcohol
(b) Secondary alcohol
(c) Tertiary alcohol
(d) all of these

Explanation: Option (b) is correct. Because when a secondary alcohol is oxidized, it loses two hydrogen atoms and forms a ketone. Primary alcohols, on the other hand, are oxidized to aldehydes and then further to carboxylic acids, while tertiary alcohols do not oxidize easily because they lack the hydrogen atom on the carbon bearing the hydroxyl group.

5. Acetone reacts with HCN to form a cyanohydrin. It is an example of:
(a) Electrophilic addition
(b) Electrophilic substitution
(c) Nucleophilic addition
(d) Nucleophilic substitution

Explanation: Option (c) is correct. Because in the reaction of acetone with HCN (hydrogen cyanide), the cyanide ion (CN⁻) acts as a nucleophile. It attacks the electrophilic carbonyl carbon of acetone (which is a ketone), resulting in the formation of a cyanohydrin. This process is a classic example of nucleophilic addition, where a nucleophile adds to the carbonyl group of the substrate.

6. Which of the following compounds will not give iodoform test on treatment with NaOH?
(a) Acetaldehyde
(b) Acetone
(c) Butanone
(d) 3-Pentanone

7. Which of the following compounds will react with Tollen’s reagent?
(a) CH₃ – C – H
(b) CH₃ – C – CH₃
(c) CH₃ – C – OH
(d) CH₃ – C – CH₂ – CH₃

Explanation: Option (b) is correct. Because

8. Cannizzaro’s reaction is not given by:
(a) Formaldehyde
(b) Acetaldehyde
(c) Benzaldehyde
(d) Trimethylacetaldehyde

Explanation: Option (b) is correct. Because Cannizzaro’s reaction happens with aldehydes that don’t have alpha-hydrogens (e.g., formaldehyde, benzaldehyde). Acetaldehyde has alpha-hydrogens and doesn’t undergo Cannizzaro’s reaction; it usually undergoes aldol condensation instead.

9. Which of the following reagents will react with both aldehydes and ketones?
(a) Grignard reagent
(b) Tollen’s reagent
(c) Fehling’s reagent
(d) Benedict’s reagent