Question

Which of the following transition metal ion is not coloured?

• A. Cu$^+$
• B. Ni$^{2+}$
• C. Co$^{2+}$
• D. V$^{3+}$

Hint:

A transition metal ion is colourless if it has a completely filled or completely empty d-orbital configuration.

Answer 1

The Correct Option is A

Transition metal ion colour stems from unpaired d-orbital electrons enabling d-d transitions. Cu$^+$ has an electronic configuration of [Ar] 3d$^{10}$, with all paired electrons, precluding d-d transitions. Consequently, it is colourless.