The reaction of $\mathrm{R}-2-\mathrm{hydroxy} \mathrm{propanal}$ with $\mathrm{HCN}$ occurs in basic medium. Among the following statements, which ones are correct?

$\left(\mathrm{a}\right)$ The product formed is chiral and exist as a racemic mixture.

$\left(\mathrm{b}\right)$ Racemisation occurs at ${\mathrm{C}}_1$ of reactant as carbonyl group is a planar group.

$\text{(c) }$Product formed exists as diastereomers.

$\left(\mathrm{d}\right)$ Basic medium increase ionization of $\mathrm{HCN}$ and increases ${\mathrm{CN}}^{-}$ ,i.e., the nucleophile.