Of the ions `Zn^(2), Ni^(2 +)` and `Cr^(3 +)` [atomic number of `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 coloured
C. all three are colourless
D. only `Cr^(+3)` is coloured, `Zn^(+2)` and `Ni^(+2)` are colourless

Answer

A

Explanation

`Zn^(+2)` ion only is colourless as it contains no unpaired electron `(3d^10 4s^0) . Ni^(+2) (3d^8 4s^0` , two unpaired electrons ), `Cr^(+3) (3d^3 4s^0)`, three unpaired electrons are coloured