Which of the following can exhibit geometrical isomerism ?
`[Co(NH_(3))_(4)Cl_(2))]`
`[Co(en)_(3)]Cl_(2)`
`[Co(en)_(2)(NO_(2))aCl]SCN`
`[Co(NH_(3)_(6)][Cr(CN)_(6)]`

Options

A. 1 and 2
B. 2 and 3
C. 3 and 4
D. 1,3 and 4

Answer

C

Explanation

(1) `cis-[Co(NH_(3))_(4)Cl_(2)]^(+)` has plane of symmetry as well as centre of symmetry , so optically inactive.
(2) `trans-[Co(en)_(2)Cl_(2)]^(+)` has plane of symmetry as well as centre of symmetry , so optically inactive.
(3 ) `cis-[co(en)_(2)Cl_(2)]^(+)` lacks plane of symmetry as well as centre of symmetry , so optically active.
(4) `[Co(en)_(3)]^(3+)` lacks axis of internal rotation, so optically active.