Q31 / 150 · MHT CET 2026 (20 April Shift 2) · Chemistry
Which of the following prediction is correct when the transition metal ion is colourless?
- Correct answerAit contains 0 unpaired electrons
- Bit contains 1 unpaired electrons
- Cit contains 2 unpaired electrons
- Dit contains 3 unpaired electrons
Solution
The colour of transition metal ions is primarily due to d-d transitions, which require the presence of partially filled d-orbitals.
When the d-orbitals are completely empty ($d^0$ configuration, e.g., $Sc^{3+}$, $Ti^{4+}$) or completely filled ($d^{10}$ configuration, e.g., $Zn^{2+}$, $Cu^+$), d-d transitions are not possible.
In both $d^0$ and $d^{10}$ configurations, there are no unpaired electrons. Therefore, a transition metal ion is colourless when it contains 0 unpaired electrons.
Answer: it contains 0 unpaired electrons
When the d-orbitals are completely empty ($d^0$ configuration, e.g., $Sc^{3+}$, $Ti^{4+}$) or completely filled ($d^{10}$ configuration, e.g., $Zn^{2+}$, $Cu^+$), d-d transitions are not possible.
In both $d^0$ and $d^{10}$ configurations, there are no unpaired electrons. Therefore, a transition metal ion is colourless when it contains 0 unpaired electrons.
Answer: it contains 0 unpaired electrons
Hence, the correct answer is option: 'A'.