Question

Formation of coloured ions is possible due to the presence of:

Hint:

Transition metal ions are coloured because of d–d transitions of unpaired electrons in partially filled d-orbitals.

Answer 1

Step 1: Why ions show colours.
The formation of coloured ions, especially in transition metals, is due to the presence of unpaired d-electrons. These electrons undergo d–d electronic transitions when light is absorbed, producing colour.

Step 2: Analyzing options.
- (A) Unpaired electrons: Correct. They are responsible for colour due to electronic transitions.
- (B) Paired electrons: Do not cause colour because no electronic transition occurs.
- (C) Non-bonded electrons: They may cause other properties but not coloured ions.
- (D) None of the above: Incorrect, since unpaired electrons are responsible.

Step 3: Conclusion.
Therefore, coloured ions are formed due to the presence of unpaired electrons.

Final Answer: \[ \boxed{\text{(A) unpaired electrons}} \]