Which one of the following compounds shows optical isomerismCH3CHCl−CH2−CH3CH3−CH2−CHCl−CH2−CH3ClCH2−CH2−CH2−CH3ClCH2−CH2−CH3

The compound that shows optical isomerism is CH3−CH2−CHCl−CH2−CH3.

Optical isomerism occurs when a molecule can form two non-superimposable mirror images, also known as enantiomers. This usually happens when a carbon atom is bonded to four different groups, making it a chiral center.

In the given compounds, only CH3−CH2−CHCl−CH2−CH3 has a carbon atom (the third one from the left) that is attached to four different groups: a hydrogen atom, a -CH2-CH3 group, a -CH2-CH3 group, and a chlorine atom. Therefore, this compound can exist as two different enantiomers, making it optically active.

The other compounds do not have any carbon atoms bonded to four different groups, so they do not show optical isomerism.