Major product of the following reaction is ${\mathrm{CH}}_3\mathrm{Br}+\mathrm{KCN}\to$

KCN being ionic in nature dissociates into K⁺ and CN⁻. CN⁻  being ambident nucleophile provides both carbon and nitrogen but attack takes place through carbon as C−C bond is stronger than C−N bond.

${\mathrm{CH}}_3\mathrm{Br}+\mathrm{KCN}\to {\mathrm{CH}}_3\mathrm{CN}+\mathrm{KBr}$