Which of the following ions will exhibit colour in aqueous solution ?

Options

A. `La^(3+)(Z=57)`
B. `Ti^(3+)(Z=22)`
C. `Lu^(3+)(Z=71)`
D. `Sc^(3+)(Z=21)`

Answer

B

Explanation

Key Idea Colour is obtained as a consequence of d-d (or f-f) translation, and for d-d (or f-f) transition, presence of unpaired electrons is the necessary conditions.
Electronic configuration of
`La^(3+) (Z=57) [Xe]4f^(0)5d^(0)6s^(0)` (no unpaired electrons)
`Ti^(3+) (Z=22)=[Ar]3d^(1)4s^(0)` (one unpiared electrons)
`Lu^(3+)(Z=72) = [Xe]4f^(14)5d^(0)6s^(0)` (no unpiared electrons)
`Sc^(3+)(Z=21) = [Ar]3d^(0)4s^(0)` (no unpaired elecrons)
Hence, due to the presence of unpaired electron in `Ti^(3+)`, it exhibit colour in aqueous solution.