Which particle may be removed from a stable neutral atom with the least energy change?

The $1^{st}$ ionization enthalpy for $Mg$ is $+737 \text{ kJ/mol}$. The most probable estimated value of the $2^{nd}$ ionization enthalpy of $Mg$ is . . . . . . .

The first ionization enthalpies of $Na, Mg$ and $Si$ are respectively $496, 737$ and $786 \ kJ \ mol^{-1}$. What would be the first ionization enthalpy of $Al$ in $kJ \ mol^{-1}$?

Which of the following electronic configurations will have the least $I.P.$ value?

$A$ sudden large jump between the values of second and third ionisation energies of an element would be associated with the electronic configuration:

The first four ionisation energy values of an element are $191$,$578$,$872$ and $5962 \ kcal$. The number of valence electrons in the element is :-