Explanation

(d)
Total number of optical isomers=$(2)^{n}$
(where n=number of asymmetric carbon atom).
$= (2)^{2} = 4$
Out of these four optical isomers two are $meso$ structures which are optically in active.
∴ Only two structures $d$ and $l$- tartaric acid are optically active.
[image:12_image360.emf]