In the long form of the periodic table,the elements having the lowest ionisation potentials are present in:

Choose the correct order of second ionisation enthalpies of Carbon,Nitrogen,Oxygen and Fluorine.

For $Mg$,the values of $\Delta_iH_1$ and $\Delta_iH_2$ are $178 \, kcal \, mol^{-1}$ and $348 \, kcal \, mol^{-1}$ respectively. The enthalpy change for the reaction $Mg \to Mg^{2+} + 2e^-$ is ............. $kcal \, mol^{-1}$.

Amongst the following elements,the highest ionization energy is

The incorrect statement is:

Discuss and compare the trend in ionisation enthalpy of the elements of group-$1$ with those of group-$17$ elements.