JEE Main 2025 · 23 January · morning · Single correct · +4 / −1
The correct set of ions (aqueous solution) with same colour from the following is:
- (a) V²⁺, Cr³⁺, Mn³⁺
- (b) Ti⁴⁺, V⁴⁺, Mn²⁺
- (c) Sc³⁺, Ti³⁺, Cr²⁺
- (d) Zn²⁺, V³⁺, Fe³⁺
Answer and solution
Answer (a) V²⁺, Cr³⁺, Mn³⁺
Solution
Chemistry ma’am · 3 steps
Write each ion's d-electron count first, then recall its colour. Only one set comes out all violet.
- Count d electrons. Remove the charge from the 4s and 3d electrons of the neutral atom. For example, V is 3d³ 4s², so V²⁺ is 3d³.
- Colourless cases. Ions with d⁰ or d¹⁰ cannot undergo a d–d transition, so they are colourless. Any set containing one of these and a coloured ion fails at once.
Option Ions (d count) Colours in water Same colour? (a) V²⁺ (d³), Cr³⁺ (d³), Mn³⁺ (d⁴) violet, violet, violet yes (b) Ti⁴⁺ (d⁰), V⁴⁺ (d¹), Mn²⁺ (d⁵) colourless, blue, pale pink no (c) Sc³⁺ (d⁰), Ti³⁺ (d¹), Cr²⁺ (d⁴) colourless, purple, blue no (d) Zn²⁺ (d¹⁰), V³⁺ (d²), Fe³⁺ (d⁵) colourless, green, yellow no - So. Only (a) has three ions of the same colour: V²⁺, Cr³⁺ and Mn³⁺ are all violet in aqueous solution.
The idea to keep. A d⁰ or d¹⁰ ion is always colourless. For the others, learn the NCERT colour table. The same d count does not guarantee the same colour: Mn²⁺ is pink but Fe³⁺ is yellow.
Answer from the NTA final answer key. Solution by PrepWiser.