Question

The number of d-electrons in $F{e}^{2+}$ (Atomic number of Fe =26) is not equal to that of the

• A. p-electrons in Ne (At. no.=10)
• B. s-electrons in Mg (At. no.=12)
• C. d-electrons in Fe
• D. p-electrons in $C{l}^{-}$ ( At. no. of Cl = 17)

Answer 1

The correct option is D p-electrons in $C{l}^{-}$ ( At. no. of Cl = 17)

Iron is a transition element (d-block). Its atomic number is 26 (= electrons).
Its electronic configuration is,
$Fe-1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^6$ or
$\left[Ar\right]4s^{2}3d^6$.

$F{e}^{2+}\to 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^6$
Thus, it has 6 d-electrons.

$C{l}^{-}\to 1s^2,2s^{2}2p^6,3s^{2}3p^6\to 12\text{p-electrons.}$
$Fe\to 1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^6\to 6\text{d-electrons}$
$Mg\to 1s^{2}2s^{2}2p^{6}3s^2\to 6\text{s-electrons}$
$Ne\to 1s^{2}2s^{2}2p^6\to 6\text{p-electrons}$

Hence,
Total number of d-electrons in $F{e}^{2+}$ is not equal to p electrons in $C{l}^{-}$