JEE Main 2022 · 29 July · morning · Single correct · +4 / −1
In following pairs, the one in which both transition metal ions are colourless is :
- (a) Sc³⁺, Zn²⁺
- (b) Ti⁴⁺, Cu²⁺
- (c) V²⁺, Ti³⁺
- (d) Zn²⁺, Mn²⁺
Answer and solution
Answer (a) Sc³⁺, Zn²⁺
Solution
Chemistry ma’am · 3 steps
Write the d-electron count for each ion: an empty or completely full d subshell means no colour.
- Where colour comes from. A transition metal ion is coloured when an electron can jump between d orbitals by absorbing visible light. This d–d transition needs a partly filled d subshell.
- The rule. A d⁰ ion has no d electron to jump, and a d¹⁰ ion has no empty d orbital to jump into. Both are colourless. Any d¹ to d⁹ ion is coloured.
Ion d configuration Colour Sc³⁺ 3d⁰ colourless Zn²⁺ 3d¹⁰ colourless Ti⁴⁺ 3d⁰ colourless Cu²⁺ 3d⁹ blue V²⁺ 3d³ violet Ti³⁺ 3d¹ purple Mn²⁺ 3d⁵ pale pink - So. Only (a) has two colourless ions: Sc³⁺ is 3d⁰ and Zn²⁺ is 3d¹⁰.
The idea to keep. For colour, check the d count after removing electrons (4s goes first). d⁰ and d¹⁰ are colourless; anything in between is coloured, even if only faintly.
Answer from the NTA final answer key. Solution by PrepWiser.