Looking for classes? Ksquare Career Institute, Bengaluru →
Which one of the following ions exhibits d-d transition and paramagnetism as well?
Explanation
Only $Mn^{6+}$ ($3d^1$) has an unpaired d-electron.
Detailed Solution
$CrO_4^{2-} \Rightarrow Cr^{6+} = [Ar]$; unpaired electrons (n) = 0; diamagnetic
$Cr_2O_7^{2-} \Rightarrow Cr^{6+} = [Ar]$; unpaired electrons (n) = 0; diamagnetic
$MnO_4^{2-} \Rightarrow Mn^{6+} = [Ar]\,3d^1$; unpaired electrons (n) = 1; paramagnetic
$MnO_4^- \Rightarrow Mn^{7+} = [Ar]$; unpaired electrons (n) = 0; diamagnetic
So $MnO_4^{2-}$ shows d-d transition and paramagnetism.
$Cr_2O_7^{2-} \Rightarrow Cr^{6+} = [Ar]$; unpaired electrons (n) = 0; diamagnetic
$MnO_4^{2-} \Rightarrow Mn^{6+} = [Ar]\,3d^1$; unpaired electrons (n) = 1; paramagnetic
$MnO_4^- \Rightarrow Mn^{7+} = [Ar]$; unpaired electrons (n) = 0; diamagnetic
So $MnO_4^{2-}$ shows d-d transition and paramagnetism.