The organic chloro compound which shows complete stereochemical inversion during a ${\mathrm{S}}_{\mathrm{N}}2$ reaction is

The reaction involving primary alkyl halide proceeds via ${\mathrm{S}}_{\mathrm{N}}2$ mechanism. This brings about complete stereochemical inversion at the carbon atom. The ${\mathrm{S}}_{\mathrm{N}}2$ mechanism is inhibited by increasing steric bulk of the groups attached to the carbon atom. The reaction may proceed via either ${\mathrm{S}}_{\mathrm{N}}1$ or ${\mathrm{S}}_{\mathrm{N}}2$ mechanism. Thus, the molecule may not show complete stereochemical inversion.