Question

Which of the following cations in their oxidation states forms colored compounds ?

• A. \(\text{Sc}^{3+}\)
• B. \(\text{Ti}^{4+}\)
• C. \(\text{Cu}^+\)
• D. \(\text{V}^{3+}\)

Hint:

Colour needs partly filled d orbitals, as in V3+ (d2).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Transition metal ions are coloured because an electron can jump between split d orbitals (a d-d transition) by absorbing visible light. This needs a partly filled d subshell.

Step 2: Check each ion:
\(\text{Sc}^{3+}\): \(3d^0\), no d electron to excite, colourless.
\(\text{Ti}^{4+}\): \(3d^0\), colourless.
\(\text{Cu}^{+}\): \(3d^{10}\), completely filled, no d-d transition, colourless.
\(\text{V}^{3+}\): \(3d^2\), partly filled, so it shows d-d transition and is coloured (green).

Final Answer:
\(\text{V}^{3+}\) forms coloured compounds, option (D). \[ \boxed{\text{V}^{3+}} \]