Reagents producing HCl gas from ethanol

Steps:

• Gas turns litmus red indicates acidic gas, specifically HCl, as it rapidly acidifies moist litmus.
• Ethanol (CH3CH2OH) reacts with chlorinating agents to form alkyl chloride and HCl gas.
• Test each reagent: sodium produces neutral H2; concentrated H2SO4 yields ethene (neutral); PCl5 gives CH3CH2Cl + POCl3 + HCl; SOCl2 gives CH3CH2Cl + SO2 + HCl.
• Thus, only reagents 3 (PCl5) and 4 (SOCl2) rapidly produce the required gas.

Why D is correct:

• Option D pairs reagents 3 and 4, both of which react with ethanol via chlorination to liberate HCl gas (e.g., ROH + PCl5 → RCl + POCl3 + HCl).

Why the others are wrong:

• A includes 1 (H2SO4, produces neutral ethene) and 2 (Na, produces neutral H2).
• B includes 1 (neutral gas) and 3 (correct but paired wrongly).
• C includes 2 (neutral H2) and 4 (correct but paired wrongly).

Final answer: D