Question

Which one of the following metal ions is colourless ?

• A. $V^{2+}$
• B. $Cr^{3+}$
• C. $Zn^{2+}$
• D. $Ti^{3+}$

Answer 1

Answer: (C)

$Zn^{2+}$

Answer 2

V(Z = 23) : $[Ar]^{18}\, 4s^23d^3$ $V^{2+}$ : $[Ar]^{18}\, 3d^3$ Cr(Z = 24) : $[Ar]^{18}\, 4s^13d^5$ $Cr^{3+}$ : $[Ar]^{18}\, 3d^5$ Zn(Z = 30) : $[Ar]^{18}\, 4s^23d^{10}$ $Zn^{2+}$ : $[Ar]^{18}\, 3d^{10}$ Ti(Z = 22) : $[Ar]^{18}\, 4s^23d^2$ $Ti^{3+}$ : $[Ar]^{18}\, 3d^1$ Thus, only $Zn^{2+}$ with no unpaired electron will be colourless.