Consier the following ions
1. `Ni^(2+)`
2. `Co^(2+)`
3. `Cr^(2+)`
4. `Fe^(3+)`
Atomic number : `Cr=24, Fe=26, Co=27, Ni=28.`
The correct sequence of increasing order of the number of unpaired electrons in these ions is

Options

A. `1,2,3,4`
B. `4,2,3,1`
C. `1,3,2,4`
D. `3,4,2,1`

Answer

A

Explanation

No. of unpaired electrons :
1. `Ni^(2+) (Z = 28) : [Ar] 3d^8 = 2`
2. `Co^(2+) (Z = 27) : [Ar] 3d^7 =3`
3. `Cr^(2+) (Z = 24) : [Ar] 3d^5 = 4`
4. `Fe^(3+) (Z = 26) : [Ar] 3d^5 = 5`
`:.` Correct order = `1,2,3,4`.