A carbonyl compound reacts with hydrogen cyanide to form cyanohydrin which on hydrolysis forms a racemic mixture of -hydroxy acid. The carbonyl compound is 
(a) acetaldehyde (b) acetone
(c) diethyl ketone (d) formaldehyde
In this reaction, by the complete hydrolysis of cyanide gives acid and partial hydrolysis gives amide.
If it is racemic mixture, therefore the C-atom must be asymmetric carbon atom.