Alcohol identification via oxidation and iodoform tests

Steps:

• Decolourisation of warm acidified KMnO4 indicates an oxidisable alcohol (primary or secondary, not tertiary).
• Yellow precipitate with alkaline I2 confirms iodoform test positivity, requiring oxidation to a methyl ketone (CH3COR) or acetaldehyde.
• For C5H12O alcohols, evaluate structures: primary alcohols oxidise to aldehydes/carboxylic acids; secondary to ketones.
• Only secondary alcohols with CH3CH(OH)R structure yield methyl ketones for iodoform reaction.

Why B is correct:

• 3-Methylbutan-2-ol (CH3CH(OH)CH(CH3)CH3) is secondary and oxidises to CH3COCH(CH3)CH3, a methyl ketone that gives iodoform (CHI3 precipitate).

Why the others are wrong:

• A: Primary alcohol oxidises to aldehyde without CH3CO- group, no iodoform.
• C: Primary alcohol oxidises to pentanoic acid, no iodoform.
• D: Secondary alcohol oxidises to pentan-3-one (CH3CH2COCH2CH3), not a methyl ketone, no iodoform.

Final answer: B