(a) Why does p-dichlorobenzene have a higher m.p than its o-and m-isomers?
(b) Why is (`pm`) - Butan -2 - ol of is optically inactive?

Explanation

(a) p-dichlorobenzene have higher melting point than ortho and meta isomer. This is because the para isomer is higher a symmetrical structure and therefore, its packing is more efficient as compared to the ortho and meta isomer, therefore, it shows higher melting point.

(b) The (±)-Butan-2-olisopticallyinactive because it exist in two enantiomeric forms which are non-superimposable mirror images of each other. Both the isomers are present in equal amounts therefore, it does not rotates the plane of polarized light and is optically inactive.