A carbonyl compound reacts with hydrogen cyanide to form cyanohydrin which on hydrolysis forms a racemic mixture of $\alpha$ -hydroxy acid. The carbonyl compound is :

The formation of a racemic mixture implies the resulting $\alpha$ -hydroxy acid possesses a chiral center. Formaldehyde, acetone, and diethyl ketone yield achiral cyanohydrins (having two identical groups attached to the $\alpha$ -carbon). Acetaldehyde (${\text{CH}}_3\text{CHO}$) forms 2-hydroxypropanoic acid (lactic acid), which has a chiral center, thereby giving a racemic mixture upon synthesis.