Question

The aqueous solution containing which one of the following ions will be colourless
(Atomic number `Sc = 21, Fe = 26, Ri = 22, Mn = 25)`
A. `Sc^(3+)`
B. `Fe^(2+)`
C. `Ti^(3+)`
D. `Mn^(2+)`

Answer 1

Correct Answer - A
a) `._(21)Sc = 1s^(2), 2s^(2)2p^(6),3s^(2)3p^(6)3d^(1),4s^(2)`
So, `Sc^(3+) = 1s^(2),2s^(2)2p^(6),3s^(2)3p^(6)`
It is colourless due to the absence of unpaired electrons in d sub-shell)
`._(26)Fe=1s^(2),2s^(2)2p^(6),3s^(2)3p^(6)3d^(6),4s^(2)`
`Fe^(2+) = 1s^(2), 2s^(2)2p^(), 3s^(2)3p^(6)3d^(6)`

It is coloured due to the presence of four unpaired electrons in d sub-shell)
`._(22)Ti=1s^(2),2s^(2)2p^(2),3s^(2)3p^(6)3d^(2),4s^(2)`
`Ti^(3+) = 1s^(2), 2s^(2)2p^(6),3s^(2)3p^(6)3d^(1)`

It is coloured due to the presence of an unpaired electron in d sub-shell)
`._(26)Mn=1s^(2),2s^(2)2p^(6),3s^(2)3p^(6)3d^(5),4s^(2)`
`Mn^(2+) = 1s^(2),2s^(2)2p^(6),3s^(2)3p^(6)3d^(5)`

It is coloured due to the presence of five unpaired electroins in d sub-shell)