Question

In which of the following paris both the ions are coloured in aqueous solution? (Atomic number, `Sc - 21, Ti = 22, Ni = 28, Cu = 29, Co = 27)`
A. `Ni^(2+)` , `Ti^(3+)`
B. `Sc^(3+)` , `Ti^(3+)`
C. `Sc^(3+) ,Co^(2+)`
D. `Ni^(2+)` , `Cu^(+)`

Answer 1

Correct Answer - A
Only those ions are coloured in aqueous solution which neither have (n - 1) `d^(0)` configuration nor have (n - 1) `d^(10)` configuration.
`Ni (3d^(8) 4s^(2)) implies Ni^(2+) (3d^(8)) implies` coloured
`Ti (3d^(2) 4s^(2)) implies Ti^(3+) (3d^(1)) implies` coloured
`Sc (3d^(1) 4s^(2)) implies Sc^(3+) (3d^(0) implies` colourless
`Co (3d^(7) 4s^(2)) implies Co^(2+) (3d^(7)) implies` coloured
`Cu (3d^(10) 4s^(1)) implies Cu^(+) (3d^(10)) implies` colourless