Of the ions `Zn^(2+),Ni^(2+) and Cr^(3+)` (atomic number Zn=30,Ni=28,Cr=24):

Options

A. Only `Zn^(2+)` is colourless and `Ni^(2+) and Cr^(3+)` are coloured.
B. all three are colourless.
C. all three are coloured
D. only `Ni^(2+)` is coloured and `Zn^(2+)` and `Cr^(3+)` are colourless.

Answer

A

Explanation

Valence shell electron configuration of `._30Zn^(+2)` is `3d^(10)4s^(0)`. As there is no unpaired electrons for d-electrons for d-d transition the solution of ion will be colourless.
Valence shell electron configuration of `._28^(2+) is 3d^(8) 4s^(0)` . As there 2 unpaired electrons , there is d-d transition of electrons , so the solution of ion will be coloured.
Valence shell electrons configuration of `._24Cr^(3+) is 3d^(3) 4s^(0)` . As there are 3 unpaired , there is d-d transition of electrons, so the solution of ions will be coloured.