In the reaction
CH3CHO + HCN → CH3−CH(OH)CN H+/H2O−−−−−−−−→ CH3−CH(OH)COOH
An asymmetric centre is generated. The acid obtained would be
50% d + 50%l - isomer
A racemic mixture is always produced whenever a new chiral carban atom is generated in a Reaction. Thus 50%d and 50% l isomers are produced.