The atomic number of the element from the following with the lowest $1^{st}$ ionisation enthalpy is:

The first ionization enthalpy of $O$ is less than that of $N$,because .........

The first ionization enthalpies of $Li$,$Be$,and $C$ are $520$,$899$,and $1086 \ kJ \ mol^{-1}$ respectively. Which of the values $800$ or $900 \ kJ \ mol^{-1}$ is more likely for the first ionization enthalpy of $B$? Why?

Which of the following elements has the lowest ionisation potential?

The five successive ionization enthalpies of an element are $800, 2427, 3658, 25024$ and $32824 \ kJ \ mol^{-1}$. The number of valence electrons in the element is

The correct order of ionisation energy of $C$,$N$,$O$,and $F$ is