In this reaction: $\begin{aligned} \mathrm{CH}_3 \mathrm{CHO}+\mathrm{HCN} & \rightarrow \mathrm{CH}_3…
In this reaction:
$\begin{aligned}
\mathrm{CH}_3 \mathrm{CHO}+\mathrm{HCN} & \rightarrow \mathrm{CH}_3 \mathrm{CH}(\mathrm{OH}) \mathrm{CN} \stackrel{\mathrm{H} . \mathrm{OH}}{\longrightarrow} & \mathrm{CH}_3 \mathrm{CH}(\mathrm{OH}) \mathrm{COOH}
\end{aligned}$
an symmetric centre is generated. The acid obtained would be:
D-isomer
L-isomer
$50 \% \mathrm{D}+50 \%$ L-isomer
$20 \% \mathrm{D}+80 \% \mathrm{~L}$-isomer
Solution
Lactic acid is an optically active compound due to presence of assymmetric carbon. It exist in D and $\mathrm{L}$ form in the ratio $1: 1$, forming a racemic mixture.
Related Theory
Enantiomers are stereoisomers which are non superimposable, mirror images. A mixture of equal amounts of two stereoisomers of an optically active substance is called a racemic mixture or racemate.