An organic compound " P " of molecular formula C₆H₁₂O₃ gives positive Iodoform test but negative Tollen's test. When " P " is treated with dilute acid, it produces " Q ". " Q " gives positive Tollen's test and also iodoform test. The structure of " P " is :

Solution

Chemistry ma’am · 3 steps

Spot the acetal: it hides an aldehyde from Tollens' reagent until dilute acid unmasks it.

1. Read the clues. P gives iodoform, so it has a CH₃CO⁻ group. P fails Tollens' test, so it has no free -CHO. Q passes Tollens' test, so dilute acid must release a -CHO that was hidden in P.
2. Hidden aldehyde. An acetal -CH(OCH₃)₂ is a protected aldehyde. It survives the basic Tollens' and iodoform reagents, but dilute acid hydrolyses it back to -CHO and 2 CH₃OH. A ketal >C(OCH₃)₂ gives back a ketone instead. Plain ethers are not hydrolysed at all.

   Option (all C₆H₁₂O₃)	P: iodoform / Tollens	Q from dilute acid	Q: Tollens / iodoform
   (a) (CH₃O)₂CHCH₂CH₂CHO	no / yes (free CHO)	succinaldehyde	yes / no
   (b) CH₃COCH(OCH₃)CH₂OCH₃	yes / no	no change (ethers stay)	no / yes
   (c) CH₃COCH₂CH(OCH₃)₂	yes / no	CH₃COCH₂CHO	yes / yes
   (d) CH₃COC(OCH₃)₂CH₃	yes / no	CH₃COCOCH₃	no / yes

   CH₃COCH₂CH(OCH₃)₂ →(dil. H₃O⁺) CH₃COCH₂CHO + 2CH₃OH

3. So. Only (c) fits every clue: P is 4,4-dimethoxybutan-2-one. Q is 3-oxobutanal, which has a -CHO for Tollens' test and a CH₃CO⁻ for the iodoform test.

The idea to keep. When a compound fails Tollens' test but its acid-hydrolysis product passes, look for an acetal -CH(OR)₂. It is a masked aldehyde that only dilute acid can unmask.

Answer from the NTA final answer key. Solution by PrepWiser.