Question

Which one of the following ions exhibits $d-d$ transition and paramagnetism as well ?

• A. $MnO _{4}^{2-}$
• B. $CrO^{2-}_4 $
• C. $MnO^{-}_4 $
• D. $Cr_2 O^{2-}_7 $

Answer 1

Answer: (A)

$CrO _{4}^{2-} \Rightarrow Cr ^{6+}=[ Ar ]$

Unpaired electron $( n )=0 ;$ Diamagnetic

$Cr _{2} O _{7}^{2-} \Rightarrow Cr ^{6+}=[ Ar ]$

Unpaired electron $( n )=0 ;$ Diamagnetic

$MnO _{4}^{2-}= Mn ^{6+}=[ Ar ] 3 d ^{1}$

Unpaired electron $( n )=1$; Paramagnetic

$MnO _{4}^{-}= Mn ^{7+}=[ Ar ]$

Unpaired electron $( n )=0$; Diamagnetic