Question

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

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

Answer 1

Answer: (B)

Electronic configuration of $F{e}^{2+}$ is [Ar] $3d^{6}4s^0$
$\therefore$ Number of $d$-electrons $=6$
$Mg=1s^{2}2s^{2}2p^{6}3s^2(6s\text{-electrons) }$
It matches with the the $6d$-electrons of $F{e}^{2+}$
$Cl=1s^{2}2s^{2}2p^{6}3s^{2}3p^5\text{ (11p-electrons) }$
It does not match with the $6d$-electrons of $F{e}^{2+}$.
$Cr=[Ar]3d^{6}4s^2(6d\text{-electrons })$
It matches with the $6d$-electrons of $F{e}^{2+}$.
$Ne=1s^{2}2s^{2}2p^6\text{ (6p-electrons) }$
It matches with the $6d$-electrons of $F{e}^{2+}$.
Hence, $Cl$ has $11p$-electrons which does not matches in number with $6d$-electrons of $F{e}^{2+}$.