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

In ${\text{S}}_{N}2$ reactions, the nucleophile attacks the carbon atom from the side opposite to the leaving group, leading to inversion of configuration.The rate of ${\text{S}}_{N}2$ reaction depends on steric hindrance. Methyl halides (${\text{CH}}_3\text{X}$) are the least hindered and react most rapidly via the ${\text{S}}_{N}2$ mechanism.Order of reactivity: ${\text{CH}}_3\text{Cl}>1^{\circ }>2^{\circ }>3^{\circ }$.Thus, methyl chloride (${\text{CH}}_3\text{Cl}$) shows the most efficient ${\text{S}}_{N}2$ reaction and complete stereochemical inversion.