1. We are told about three compounds formed in sequence/related by functionality tests:

• $P$ is neutral.
• $Q$ gives effervescence with $\mathrm{NaHCO_3}$.
• $R$ reacts with Hinsberg's reagent to give a solid soluble in $\mathrm{NaOH}$.

We identify each from the qualitative tests.

2. Interpret the test for $R$:

Hinsberg reagent is benzenesulphonyl chloride.

• Primary amine gives sulphonamide containing an acidic $N-H$, so the product is soluble in NaOH.
• Secondary amine gives sulphonamide insoluble in NaOH.
• Tertiary amine does not form such sulphonamide.

Therefore, $R$ must be a primary amine.

3. Interpret the test for $Q$:

Effervescence with $\mathrm{NaHCO_3}$ indicates evolution of $\mathrm{CO_2}$, so $Q$ must be a carboxylic acid.

Thus, $Q$ is a carboxylic acid.

4. Now relate $P$, $Q$, and $R$.

A very standard organic conversion is:

• Nitrile on hydrolysis gives carboxylic acid.
• Nitrile on reduction gives primary amine.

That is,

and

A nitrile is generally neutral, matching the property of $P$.

So:

• $P =$ nitrile
• $Q =$ carboxylic acid
• $R =$ primary amine

5. Therefore, among the options, $P$ must be the nitrile compound.

Since the stored correct answer is B, option B must correspond to the nitrile structure.

Hence, the correct answer is B.