A carbonyl compound reacts with hydrogen to form a cyanohydrin which on hydrolysis forms a racemic mixture of α-hydroxy acids. The carbonyl compound is:

Formaldehyde  Acetaldehyde  Acetone  Diethyl ketone

Acetaldehyde

Acetaldehyde reacts with hydrogen cyanide $(HCN)$ to form cyanohydrin {CH3​CH(OH)CN} which on hydrolysis forms a racemic mixture of $\alpha -$ hydroxy acid {CH3​CH(OH)COOH}  As the cyanohydrin of acetaldehyde contains chiral centre so we will get racemic mixture.