Identify the product ' B ' in the following sequence of reactions. Methylpropanoate $\underset{\text { dil. } \mathrm{NaOH}}{\stackrel{\Delta}{\longrightarrow}} \mathrm{A} \xrightarrow[\text { Conc. } \mathrm{HCl}]{\mathrm{H}^{+}} \mathrm{B}$

Hydrolysis of methylpropanoate with dilute sodium hydroxide yields sodium propanoate via saponification:

$\mathrm{CH_3 CH_2 COOCH_3 + NaOH \rightarrow CH_3 CH_2 COONa + CH_3 OH}$

Subsequent acidification with concentrated hydrochloric acid converts the salt to propanoic acid:

$\mathrm{CH_3 CH_2 COONa + H+ \rightarrow CH_3 CH_2 COOH + Na+}$

Thus product B is propanoic acid, corresponding to option D.