Question:
Which of the following ions forms coloured solution?
Which of the following ions forms coloured solution?
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A transition-metal ion is coloured only if it has partially filled d-orbitals; d0 and d10 ions are colourless.
Updated On: Jul 10, 2026
- Ti4+
- Fe3+
- Zn2+
- Cu+
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The Correct Option is B
Solution and Explanation
Step 1: Colour in transition metal ions arises from d-d electronic transitions. This requires the d-orbitals to be partially filled (some unpaired d electrons). Ions with empty (d0) or completely filled (d10) d-orbitals are colourless because no d-d transition is possible.
Step 2: Write the configurations. Ti4+ = [Ar]3d0 (no d electron, colourless). Fe3+ = [Ar]3d5 (five unpaired d electrons, coloured). Zn2+ = [Ar]3d10 (filled, colourless). Cu+ = [Ar]3d10 (filled, colourless).
Step 3: Only Fe3+ has partially filled d-orbitals, so only its solution is coloured.
Conclusion: Option (ii) Fe3+ is correct.
Step 2: Write the configurations. Ti4+ = [Ar]3d0 (no d electron, colourless). Fe3+ = [Ar]3d5 (five unpaired d electrons, coloured). Zn2+ = [Ar]3d10 (filled, colourless). Cu+ = [Ar]3d10 (filled, colourless).
Step 3: Only Fe3+ has partially filled d-orbitals, so only its solution is coloured.
Conclusion: Option (ii) Fe3+ is correct.
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