Sodium metal selectively reacts with alcohols

Steps:

• Identify the target functional group: alcohols in a mixture with alkanes (saturated) and alkenes (unsaturated).
• Recall reagents for alcohols: sodium metal (Na) reacts to produce hydrogen gas, observable as effervescence.
• Eliminate reagents for alkenes: bromine (Br₂) and KMnO₄ test for unsaturation via decolorization.
• Rule out carbonyl-specific test: 2,4-dinitrophenylhydrazine reacts with aldehydes/ketones, not alcohols.

Why A is correct:

• Sodium (Na) reacts with alcohols via 2ROH + 2Na → 2RONa + H₂, producing visible hydrogen bubbles, while alkanes and alkenes do not react.

Why the others are wrong:

• B: Br₂ (in CCl₄) decolorizes with alkenes due to addition reaction, not specific to alcohols.
• C: KMnO₄ (aq) oxidizes alkenes, causing purple color loss, but ignores alcohols.
• D: 2,4-Dinitrophenylhydrazine forms hydrazones with carbonyls, irrelevant to alcohols.

Final answer: A