Question

The ion that has different number of electrons in the ultimate and penultimate shells is :

• A. $N{a}^{+}$
• B. $K^{+}$
• C. $C{l}^{-}$
• D. $C{a}^{2+}$

Answer 1

Answer: (A)

$N{a}^{+}$

The electronic configuration of ions are as follows:

$N{a}^{+}:1s^{2}2s^{2}2p^6$

$K^{+}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

$C{l}^{-}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

$C{a}^{2+}:1s^{2}2s^{2}2p^{6}3s^{2}3p^6$

The last shell is known as the ultimate shell and the shell before the last shell is the penultimate shell.

In $N{a}^{+}$ ion, the ultimate shell has 8 electrons and the penultimate shell has 2 electrons.

While in all other ions, i.e., $K^{+},C{l}^{-},C{a}^{2+}$ ultimate shell has 8 electrons and penultimate shell also has 8 electrons.