MHT CET Chemistry Question (2026) — Solution

Step-by-step 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