Question

Out of the following ions which one is colourless?

• A. $T{i}^{3+}$
• B. $V^{3+}$
• C. $C{o}^{2+}$
• D. $S{c}^{3+}$

Answer 1

The correct option is D $S{c}^{3+}$

Those ion which has unpaired electrons in d orbital can exhibit colour due to d-d transition.
Those with fully filled or empty d orbitals are colourless.
In $S{c}^{3+}{:}_{18}\left[Ar\right]3d^0$
there are no electrons in 3d and the other orbitals all are completely filled, and hence it is colourless.