Question

Which one of the following is a diamagnetic ion ?

• A. $Co^{2+}$
• B. $Cu^{2+}$
• C. $Mn^{2}$+
• D. $Sc^{3+}$

Answer 1

Answer: (D)

$Sc^{3+}$

Answer 2

$Co^{2+}$ (Z = 27) : $[Ar]^{18}\, 3d^7$ (3 unpaired electrons)
$Cu^{2+}$ (Z = 29) : $[Ar]^{18} 3d^9$ (1 unpaired electrons)
$Mn^{2+}$ (Z = 25): $[Ar]^{18} \, 3d^5$ (5 unpaired electrons)
$Sc^{3+}$ (Z = 21): $[Ar]^{18} \, 3d^0$ (No unpaired electron)
$Sc^{3+}$ with no unpaired electron will be diamagnetic