Question

The number of d-electrons in Fe²⁺ (Z = 26) is not equal to the number of electrons in which one of the following?
(a) p-electrons in Cl (Z = 17)
(b) d-electrons in Fe (Z = 26)
(c) p-electrons in Ne (Z = 10)
(d) s-electrons in Mg (Z = 12)

Answer 1

p-electrons in Cl( Z=17)

Electronic configuration of Fe2+ is [Ar]3d6 4s0

therefore, Number of electrons = 6

Mg- 1s2 2s2 2p6 (6s electrons)

It matches with the 6d electrons of Fe2+

Cl- 1s2 2s2 2p6 3s2 3p5 (11 p electrons)

It does not match with the 6d electrons of Fe2+

Fe- [Ar] 3d6 4s2 (6d electrons)

It does not match with the 6d electrons of Fe2+

Ne- 1s2 2s2 2p6 3s2 3p 6 (6p electrons)

It matches with the 6d electrons of Fe2+.

Hence, Cl has 11 p electrons which do not match in number with 6d electrons of Fe2+