Question Analysis: Assertion-Reasoning type question based on NCERT Chemistry, Class 12, Chapter 10 (Haloalkanes and Haloarenes).
Step 1 (Evaluation of Assertion): [0.5 Mark]
The Assertion states that phosphorus halides ($PX_3$ or $PX_5$) are preferred over thionyl chloride ($SOCl_2$). This is incorrect. In organic synthesis, thionyl chloride is actually preferred because the by-products formed are gases ($SO_2$ and $HCl$), which escape the reaction mixture, leaving behind pure alkyl halides.
Step 2 (Evaluation of Reason): [0.5 Mark]
The Reason states that the reaction of alcohols with thionyl chloride forms pure alkyl halides. This is correct. The reaction is represented as:
$$R-OH + SOCl_2 \xrightarrow{\text{Pyridine}} R-Cl + SO_2(g) \uparrow + HCl(g) \uparrow$$Since the by-products are gaseous, the purification of the alkyl halide is not required, making this the best method for preparing alkyl chlorides.
Step 3 (Final Concluded Answer): [1 Mark]
Conclusion: Assertion (A) is False, but Reason (R) is True.
Correct Option: (d)
💡 EL10 Concept Insight: Think of thionyl chloride like a "self-cleaning" chemical; because its waste products are gases that float away, you are left with a clean, pure product without having to do any extra work to filter it out!