A neutral fruity-smelling liquid $\mathrm{C}{}_4\mathrm{H}{}_8\mathrm{O}{}_2$ gives no effervescence with $\mathrm{NaHCO}{}_3$, no hydrogen with sodium and no silver mirror. On boiling with aqueous NaOH it gives ethanol and sodium ethanoate. The liquid is

A neutral ester is indicated by the fruity smell and absence of acid or alcohol reactions. Alkaline hydrolysis of an ester gives the alcohol part and the carboxylate, here ethanol and ethanoate, so the ester is $\mathrm{CH}{}_3\mathrm{COOC}{}_2\mathrm{H}{}_5$. Methyl propanoate would give methanol; propyl methanoate would also reduce Tollens reagent; butanoic acid effervesces.