The Aldehyde CH3CH2CHO (A) reacts with HCN to give a racemic mixture, name the compound CH3CH2CH(CN)OH (B) formed and explain why we get a racemic mixture and how we could differentiate between two different enantiomerically pure solutions of B

B = R/S 2-hydroxybutanenitrile
we get a racemic mixture because the carbon in the aldehyde where the nucleophile attacks has a trigonal planar geometry and so there is an equal chance of attack by the nucleophile from either side of the aldehyde to give two products which are not superimposable upon each other.
Each solution would rotate plane polarised light by equal amounts but in opposite directions.