Explanation

(d)
The structure of butane-2, 3-idol is as
[image:12_image302.emf]
$\because$ Optical isomers in compounds have similar asymmetric carbon atom, which are even in number $= 2^{n} - 1$
Here, $n = 2$
∴ Total number of optically active stereoisomers
$= 2^{2} - 1 = 3$