The organic chloro compound, which shows complete stereochemical inversion during a SN2 reaction, is

In SN2 reactions, the nucleophile attacks from the backside resulting in the inversion of molecule. As we move from 1° alkyl halide to 3° alkyl halide, the crowding increases and +I effect increases. This causes the carbon-bearing halogen less positively polarised. So it is less readily attacked by the nucleophile.