The ionization energy of nitrogen is more than that of oxygen because

Discuss the trend of the first ionisation enthalpy in the same period and explain why it occurs.

The order of first ionization potentials of elements $Li, Be, B, Na$ is:

Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The first ionization enthalpy for oxygen is lower than that of nitrogen.
Reason $R$: The four electrons in $2p$ orbitals of oxygen experience more electron-electron repulsion.
In the light of the above statements,choose the correct answer from the options given below.

If first ionization enthalpy $(\Delta_i H)$ values of $Na$,$Mg$ and $Si$ are respectively $496$,$737$ and $786 \ kJ \ mol^{-1}$,the first ionization enthalpy value of $Al$ (in $kJ \ mol^{-1}$) will be

Which of the following represents the correct order of increasing first ionization enthalpy for $Ca, Ba, S, Se$ and $Ar$?