Question

Among the following, incorrect order is:

• A. $I.E_1\left(Al\right)<I.E_1\left(Si\right)$
• B. $I.E_1\left(Na\right)<I.E_1\left(Mg\right)$
• C. $I.E_2\left(Mg\right)>I.E_2\left(Na\right)$
• D. $I.E_2\left(Mg\right)<I.E_2\left(Na\right)$

Answer 1

The correct option is C $I.E_2\left(Mg\right)>I.E_2\left(Na\right)$

Electronic configuration for the given species are:
${}_{11}\left[Na\right]:1s^2,2s^2,2p^6,3s^1$
${}_{12}\left[Mg\right]$: $1s^2,2s^2,2p^6,3s^2$
​​​​​​​${}_{13}\left[Al\right]$: $1s^2,2s^2,2p^6,3s^2,3p^1$
​​​​​​​${}_{14}\left[Si\right]$: $1s^2,2s^2,2p^6,3s^2,3p^2$

$Si$ has higher first ionisation energy than $Al$ because it has high $Z_{eff}$ than $Al$.

$I.E_1\left(Mg\right)>I.E_1\left(Na\right)$
Since $Mg$ has filled stable electronic configuration and has higher $Z_{eff}$, hence more energy is required to ionise $Mg$.

2nd ionisation energy of sodium is higher than magnesium because of extra stable inert gas electronic configuration attaned by $N{a}^{+}$ ion, very high energy is requied to remove an electron.
$M{g}^{+}$: $1s^2,2s^2,2p^6,3s^1$
$N{a}^{+}:1s^2,2s^2,2p^6:\left[Ne\right]$

​​​​​​​$\therefore I.E_2\left(Mg\right)<I.E_2\left(Na\right)$