The correct statement regarding nucleophilic substitution reaction in a chiral alkyl halide is:-

Recemisation occurs in $S_{N}1$ reaction and inversion occurs in  $S_{N}2$ reaction

Retention occurs in $S_{N}1$ reaction and inversion occurs in $S_{N}2$ reaction

Racemisation occurs in $S_{N}1$ reaction and retention occurs in $S_{N}2$ reaction

Recemisation occurs in both $S_{N}1 and S_{N}2$ reactions