• Preparation of Acyl Chlorides:
• Converting benzoic acid ($ ext{C}_6 ext{H}_5 ext{COOH}$) to benzoyl chloride ($ ext{C}_6 ext{H}_5 ext{COCl}$) is achieved using Thionyl Chloride ($ ext{SOCl}_2$):

$$\text{C}_6\text{H}_5\text{COOH} + \text{SOCl}_2 \longrightarrow \text{C}_6\text{H}_5\text{COCl} + \text{SO}_2\uparrow + \text{HCl}\uparrow$$

• Thionyl chloride is ideal because both by-products ($ ext{SO}_2$ and $ ext{HCl}$) are gases that escape from the reaction mixture, driving the reaction to completion and simplifying product isolation.
• Conclusion: $\text{SOCl}_2$ is used to prepare benzoyl chloride (Option 3).

Correct option: (3) SOC,