Identifying compound Y via iodoform and oxidation tests

Steps:

• Yellow precipitate with alkaline aqueous iodine indicates positive iodoform test for compounds with CH₃CO- or CH₃CH(OH)- groups.
• Color change (orange to green) with warm acidified K₂Cr₂O₇ indicates oxidation of alcohols or aldehydes, not ketones.
• Compound Y must undergo both reactions, ruling out non-oxidizable iodoform-positive compounds like ketones.
• Thus, Y is a secondary alcohol such as propan-2-ol, fitting both tests.

Why B is correct:

• B (propan-2-ol, CH₃CH(OH)CH₃) gives iodoform (oxidizes to acetone, forming CHI₃) and reduces dichromate to Cr³⁺ (green) while forming acetone.

Why the others are wrong:

• A (propanone): Positive iodoform but ketones resist dichromate oxidation, no color change.
• C (propanoic acid): No iodoform reaction; already oxidized, no dichromate reduction.
• D (ethene): No iodoform or easy oxidation by dichromate.

Final answer: B