Question

Out of the following ions Ti³⁺, V³⁺, Cu⁺, Sc³⁺, Mn²⁺, Fe³⁺ and Co²⁺ the colourless ions will be

• A. Cu⁺, Sc³⁺
• B. Ti³⁺, V³⁺
• C. Cu⁺, Co²⁺
• D. Sc³⁺, Fe³⁺

Answer 1

Answer: (A)

Only those ions will be coloured which have incomplete d - orbitals. Ions which has complete or vacant d - orbitals are colourless.

Ti3+ = [Ar] 3d1	Purple
V3+ = [Ar] 3d2	Green
Cu+ = [Ar] 3d10	Colourless
Sc3+ = [Ar]	Colourless
Mn2+ = [Ar] 3d5	Pink
Fe3+ = [Ar] 3d5	Brown
Co2+ = [Ar] 3d7	Pink

As Sc³⁺ and Cu⁺ have 3d⁰ and 3d¹⁰ configuration in their valence shell so their aqueous solutions are colourless. All others, i.e., Ti³⁺, V³⁺, Mn²⁺, Fe³⁺ and Co²⁺ are coloured in aqueous medium.