The lanthanide ion that would show colour is :

Options

A. `Lu^(3+)`
B. `La^(3+)`
C. `Gd^(3+)`
D. `Sm^(3+)`

Answer

D

Explanation

Electronic configuration of following lanthanide ions are given below.
`lu^3:4f^(14)` (colorless, no unpaired electron)
`la^(3+):4f^(0)` (colorless, no unpaired electron)
`Gd^(3+):4f^(7)` colourless
`"sm"^(3+):4f^(5)` (yellow, 5 unpaired electrons)
Ions having f electrons show colour. of these ions may be attributed to presence of f electrons.