The general formula of alkyl halide is

General formula of alkanes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+2}}\text{.}$ In case of alkyl halide, one halide (X) is replaced by one hydrogen atom and general formula of alkyl halide becomes ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n+1}}\text{X.}$