Question

The number of d-electrons in ${Fe^{2+} (Z=26)}$ is not equal to the number of electrons in which one of the following?

• A. d-electrons in Fe (Z=26)
• B. p-electrons in Ne (Z=10)
• C. s-electrons in Mg (Z=12)
• D. p-electrons in Cl (Z=17)

Answer 1

Answer: (D)

p-electrons in Cl (Z=17)

Answer 2

Electronic configuration of the elements are:
$F e ^{2+}: 1 s ^{2} 2 s ^{2} 2 p ^{6} 3 s ^{2} 3 p ^{6} 3 d ^{6}$
number of d-electrons $=6$ $F e ^{2+}: 1 s ^{2} 2 s ^{2} 2 p ^{6} 3 s ^{2} 3 p ^{6} 4 s ^{2} 3 d ^{6}$ -has 6 electrons in d-orbital i.e. same as in $d -$ robital of $F e ^{2+}$
$N e : 1 s ^{2} 2 s ^{2} 2 p ^{6}$ -has 6 electrons in p-orbital i.e. same as in d- robital of $Fe ^{2+}$
$M g : 1 s ^{2} 2 s ^{2} 2 p ^{6} 3 s ^{2}$ -has $(2+2+2) 6$ electrons in s-orbital i.e. same as in $d -$ robital of $F e ^{2+}$
$C l : 1 s ^{2} 2 s ^{2} 2 p ^{6} 3 s ^{2} 3 p ^{5}$ -has (6+5) 11 electrons in p-orbital and are not same as in d- robital of
$F e ^{2+}$