Board-style MCQs and past-paper questions in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved questions & self-assessment (past papers)
How do you distinguish an aldehyde from a ketone?
Add Tollens' reagent (ammoniacal AgNO₃) and warm gently. An aldehyde reduces it to give a bright silver mirror on the inside of the tube; a ketone gives no change. Fehling's solution gives a brick-red Cu₂O precipitate with aliphatic aldehydes only.
→ silver mirror / brick-red precipitate = aldehyde; no reaction = ketone.
Why are aldehydes more reactive than ketones in nucleophilic addition?
Two reasons. Electronic: a ketone has two electron-donating alkyl groups (+I effect) that reduce the δ+ charge on the carbonyl carbon, so it attracts the nucleophile less. Steric: the two bulky groups on a ketone hinder the nucleophile's approach. An aldehyde has only one alkyl group and a small H.
→ aldehydes are less hindered and more δ+ → more reactive.
Which compounds give a positive iodoform test, and what is the result?
Compounds with a CH₃CO– group (methyl ketones) or a CH₃CH(OH)– group, plus ethanal and ethanol. With I₂/NaOH they form a pale-yellow precipitate of iodoform, CHI₃ (antiseptic smell).
e.g. acetone, acetaldehyde, ethanol, propan-2-ol → yellow CHI₃; propanal and benzaldehyde do not.