Which of the following ions exhibits d-d transitions and paramagnetism as well?

Options

A. `CrO_(4)^(2-)`
B. `Cr_(2) O_(7)^(2-)`
C. `MnO_(4)^(-)`
D. `MnO_(4)^(2-)`

Answer

D

Explanation

d-d transition is possible only for `d^(1)` to `d^(9)` configurations while paramagnetism requires the presence of at least one uppaired electron.
`Cr (3 d^(5) 4s^(1))` and `Mn (3 d^(5) 4 s^(2))`
`CrO_(4)^(-) implies Cr (+6) implies 3 d^(0)`
`Cr_(2) O_(7)^(2-) implies Cr (+6) rarr 3 d^(0)`
`MnO_(4)^(-) implies Mn (+7)implies 3 d^(0)`
`MnO_(4)^(2-)implies 3 d^(1)`
Due ot one upaired electron, `MnO_(4)^(2-)` is paramagnetic. This upaired electron can be excited from `t_(2g)` to `e_(g)` energy level leading to d-d transition: