- ✓$Na < Mg > Al < Si$
- B$Na < Mg < Al < Si$
- C$Na > Mg > Al > Si$
- D$Na < Mg < Al > Si$
Removal of an electron from stable, fully filled orbital requires more energy than removal of electron from partially filled orbital. Thus, ionisation enthalpy for $Mg$ is greater than ionisation enthalpy for $Al$. So, the correct order of first ionization enthalpies is: $Na \,<\, Mg\, >\, Al\, <\, Si$
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$\mathop {\mathop C\limits^ \oplus {H_3}}\limits_{(a)} $ $\mathop {\begin{array}{*{20}{c}}
{C{H_2} - \mathop C\limits^ \oplus {H_2}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,F\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}}\limits_{(b)} $ $\mathop {\begin{array}{*{20}{c}}
{C{H_2} - \mathop C\limits^ \oplus {H_2}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{Br\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}}\limits_{(c)} $ $\mathop {\begin{array}{*{20}{c}}
{C{H_2} - \mathop C\limits^ \oplus {H_2}} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,C{H_3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}}\limits_{(d)} $
$4s$ $3d$
$\begin{array}{*{20}{c}} {N \equiv C} \\ {N \equiv C}\end{array}\,\,\left. {} \right\rangle C = C\,\left\langle {} \right.\,\begin{array}{*{20}{c}} {C \equiv N} \\ {C \equiv N} \end{array}$
${{O}_{(g)}}+{{e}^{-}}=O_{(g)}^{-}\Delta {{H}^{o}}=-142\ kJ\,mo{{l}^{-1}}$
$O_{(g)}^{-}+{{e}^{-}}=O_{(g)}^{2-}\Delta {{H}^{o}}=844\ kJ\,mo{{l}^{-1}}$