Question: The correct formula of Hinsberg's reagent is:

Step 1 (Definition & Identification): [0.5 Mark]

Hinsberg's reagent is chemically known as Benzenesulfonyl chloride. It is a sulfonating agent used in the laboratory for the detection and differentiation of primary, secondary, and tertiary amines. The chemical structure consists of a benzene ring attached to a sulfonyl group ($-\text{SO}_2\text{Cl}$).

Step 2 (Structural Analysis): [0.25 Mark]

• (A) $\text{C}_6\text{H}_5\text{COCl}$ is Benzoyl chloride.
• (B) $\text{C}_6\text{H}_5\text{SO}_2\text{Cl}$ is Benzenesulfonyl chloride.
• (C) $\text{C}_6\text{H}_5\text{CONHCH}_3$ is N-methylbenzamide.
• (D) $\text{C}_6\text{H}_5\text{CH}_2\text{NH}_2$ is Benzylamine.

Comparing the options with the definition, option (B) matches the chemical identity of Hinsberg's reagent.

Step 3 (Final Concluded Answer): [0.25 Mark]

The correct option is (B).

💡 EL10 Concept Insight: Think of Hinsberg's reagent as a "chemical detective" that reacts with different types of amines to create unique products; because it contains a sulfur-oxygen bond ($\text{SO}_2$), it acts as a specific tag that helps us tell primary, secondary, and tertiary amines apart based on whether they dissolve in base or not.