Question

Which of these ions is expected to be coloured in aqueous solution?
I. ${Fe}^{3+}$
II. ${Ni}^{2+}$
III. ${Al}^{3+}$

• A. I and II
• B. II and III
• C. I and III
• D. I, II and III

Answer 1

The correct option is A I and II

I. $F{e}^{2+}:\left[Ar\right]3d^6$, i.e., 4 unpaired electrons

$\therefore$ Coloured ion, [ref. image I]

II. $N{i}^{2+}:\left[Ar\right]3d^8$, i.e., 2 unpaired electrons

$\therefore$ Coloured ion, [ref. image II]

III. $A{l}^{3+}=\left[Ne\right]$, i.e., no unpaired electron in 3d, colourless ion.