The elements which occupy the peaks of the ionisation energy curve are

How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?

For an element,the values of $IP_1, IP_2, IP_3, IP_4$ and $IP_5$ are $7.1, 14.3, 34.5, 46.8$ and $162.2 \ eV$ respectively. Which of the following is the most likely element?

The successive ionisation energy values for an element $X$ are given below. Element $X$ belongs to which group?
$1^{st} \text{ IE} = 410 \ kJ \ mol^{-1}$
$2^{nd} \text{ IE} = 820 \ kJ \ mol^{-1}$
$3^{rd} \text{ IE} = 1100 \ kJ \ mol^{-1}$
$4^{th} \text{ IE} = 1500 \ kJ \ mol^{-1}$
$5^{th} \text{ IE} = 3200 \ kJ \ mol^{-1}$

Which of the following has the highest first ionisation energy?

For which of the following reactions is the $\Delta H^o$ value equal to the first ionization energy of $Ca$?