Identify product 'B' in the following sequence of reactions....

Aniline reacts with $\text{NaNO}_2$ and $\text{HCl}$ at $273\ \text{K}$ to undergo diazotization, forming benzenediazonium chloride as product A.

$\text{C}_6\text{H}_5\text{NH}_2 \xrightarrow{\text{NaNO}_2 + \text{HCl},\ 273\ \text{K}} \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^-$ (Product A)

Benzenediazonium chloride (A) on heating with water undergoes hydrolysis to yield phenol as product B along with the evolution of nitrogen gas.

$\text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- \xrightarrow{\text{H}_2\text{O},\ \Delta} \text{C}_6\text{H}_5\text{OH} + \text{N}_2\uparrow + \text{HCl}$

Thus, product B is phenol.

Answer: Phenol