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

The electronic configurations of elements $A, B$ and $C$ are $[He] 2s^1$,$[Ne] 3s^1$ and $[Ar] 4s^1$ respectively. Which one of the following orders is correct for the first ionization potentials (in $kJ \ mol^{-1}$) of $A, B$ and $C$?

Assertion $(A)$: $16$th group elements have higher ionisation enthalpy values than $15$th group elements in the corresponding periods.
Reason $(R)$: $15$th group elements have half-filled stable electronic configurations.

Assertion $(A)$: Boron has a smaller first ionisation enthalpy than beryllium.
Reason $(R)$: The penetration of a $2s$-electron to the nucleus is more than the $2p$-electron; hence,the $2p$-electron is more shielded by the inner core of electrons than $2s$-electrons.

An atom with high electronegativity has

Which of the following pairs has a higher ionization enthalpy?
$(i)$ $Ne$ or $Ar$ $(ii)$ $Cl$ or $F$ $(iii)$ $F$ or $O$ $(iv)$ $N$ or $O$
$(v)$ $Na$ or $K$ $(vi)$ $Cl$ or $S$ $(vii)$ $Kr$ or $Xe$ $(viii)$ $P$ or $S$