Question

Which one of the following is not coloured?

• A. Cu\(^{2+}\)
• B. Cu\(^+\)
• C. Ni\(^{2+}\)
• D. Fe\(^{3+}\)

Hint:

Ions with d\(^0\) (e.g., Sc\(^{3+}\)), d\(^{10}\) (e.g., Zn\(^{2+}\), Cu\(^+\)), and d\(^5\) high spin (e.g., Mn\(^{2+}\)) may be colourless or faintly coloured depending on ligands.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Colour in transition metal ions arises from d-d transitions, which require unpaired electrons or vacant d-orbitals.
Step 2: Detailed Explanation:
\begin{itemize} \item Cu\(^{2+}\): d\(^9\) configuration, one unpaired electron, coloured (blue). \item Cu\(^+\): d\(^{10}\) configuration, fully filled, no d-d transitions possible, colourless. \item Ni\(^{2+}\): d\(^8\) configuration, two unpaired electrons, coloured (green). \item Fe\(^{3+}\): d\(^5\) configuration, five unpaired electrons, coloured (yellow/brown). \end{itemize}
Step 3: Final Answer:
Cu\(^+\) is colourless, option (B).