Question

The number of optically active isomers of tartaric acid are:

• A. 1
• B. 3
• C. 4
• D. 2

Answer 1

Answer: (D)

Optical isomerism is shown by compounds in which at least one asymmetric carbon atom and it should not have plane of symmetry. Tartaric acid has 2 asymmetric carbon atoms.
Total no. of optical isomers $=(2{)}^n$
(where $n=no.$ of asymmetric carbon atom).
$=(2{)}^2=4$
Out of these 4 optical isomers two are meso structures which are optically in active.
$\therefore$ Only 2 structures d and $l$ tartaric acid are optically active.