Ionisation energy in group $I$ elements varies in the decreasing order as:

The correct order of $IE_2$ is

Which of the following electronic configurations has the highest ionization enthalpy?

Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

First and second ionization enthalpies of lithium are $520 \text{ kJ mol}^{-1}$ and $7297 \text{ kJ mol}^{-1}$ respectively. Energy required to convert $3.5 \text{ mg}$ lithium $(g)$ into $Li^{2+}(g)$ [$Li(g) \rightarrow Li^{2+}(g)$] is . . . . . . $\text{kJ}$. (nearest integer) [Molar mass of $Li = 7 \text{ g mol}^{-1}$]

Which of the following presents the correct order of second ionization enthalpies of $C$,$N$,$O$ and $F$?