Which one of the following complexes shows optical isomerism ?

Options

A. `[Co(NH_(3))_(3)Cl_(3)]`
B. `[Co(en_(2))Cl_(2)]Cl`
C. trans `[Co(en_(2))Cl_(2)]Cl`
D. `[Co(NH_(3))_(4)Cl_(2)]Cl` (en = ethylenediamine)

Answer

B

Explanation

`[Co(NH_(3))_(3)Cl_(3)]` has two geometrical isomers but both are optically inactive due to plane of symmetry.
cis `[Co(en)_(2)Cl_(2)]Cl` is optically active.
trans `[Co(en)_(2)Cl_(2)]Cl` is optically inactive due to plane of symmetry.
`[Co(NH_(3))_(4)Cl_(2)]Cl` has two geometrical isomers but both are optically inactive due to plane of symmetry.