A student is given one compound among the following compounds that gives positive test with Tollen's reagent.
The compound is :

Solution

Chemistry ma’am · 4 steps

Find the carbon carrying both the ring O and an OH: that hemiacetal opens up into a free aldehyde.

1. What Tollens' needs. Tollens' reagent, [Ag(NH₃)₂]⁺, is a mild oxidant in basic solution. It gives a silver mirror only with a free -CHO group, or with a group that can open into one in that basic medium.
2. Look at C2. In each ring, check the carbon next to the ring oxygen. A carbon that holds both the ring O and an -OH is a cyclic hemiacetal, and it is in equilibrium with the open-chain aldehyde.

   Compound	What it is	Can it open to -CHO in base?
   A	acetal: C2 carries ring O and -OCH₃	No, acetals are stable in base
   B	ether: -OCH₃ on C3	No
   C	hemiacetal: C2 carries ring O and -OH	Yes, gives HOCH₂CH₂CH₂CHO
   D	secondary alcohol: -OH on C3	No

3. Ring opening. In C, the ring C–O bond breaks and the C2 -OH becomes C=O, giving 4-hydroxybutanal. Its free -CHO is oxidised to -COO⁻ while Ag⁺ is reduced to a silver mirror.
4. So. Only compound C gives a positive Tollens' test, which is option (d).

The idea to keep. A cyclic hemiacetal is a hidden aldehyde: it opens to a free -CHO and reduces Tollens' reagent. Turn that -OH into -OR and the acetal stays locked in base.

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