CBSE Class 12 Chemistry 2025: question 1

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1. Colour in transition metal ions arises from d–d transitions, which need a partly filled d subshell.

2. $\mathrm{C}{\mathrm{u}}^{+}$ is $3d^{10}$, a completely filled subshell, so no d–d transition is possible and the ion is colourless. $\mathrm{N}{\mathrm{i}}^{2+}$ ($3d^8$), $\mathrm{C}{\mathrm{o}}^{2+}$ ($3d^7$) and ${\mathrm{V}}^{3+}$ ($3d^2$) all have unpaired electrons and are coloured.

   1 mark

Answer: (A) $\mathrm{C}{\mathrm{u}}^{+}$

Revise the chapter

• Chapter: The d- and f-Block Elements (notes, formulas, where marks are lost and every past question)
• Topic: Magnetic Properties and Colour of Transition Metal Ions