The $IE_1$ and $IE_2$ of three elements $A$,$B$,and $C$ are given as : ( $IE$ in $kJ/mol$ )

Element	$A, B, C$
$IE_1$	$400, 550, 1150$
$IE_2$	$2650, 1070, 2090$

Identify the element which represents a nonmetal.

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 of $O$ is lower than that of $N$ and $F$.
Reason $R$: The loss of an electron from $O$ leads to a stable half-filled $p$ orbital.
In light of the above statements, choose the most appropriate answer from the options given below:

The correct order of $C$, $N$, $O$ and $F$ in terms of second ionisation potential is

For which of the following reactions is the $\Delta H^o$ value equal to the first ionization energy of $Ca$?

The first,second and third ionisation energies ($E_1, E_2$ and $E_3$) for an element are $7 \ eV$,$12.5 \ eV$ and $42.5 \ eV$ respectively. The most stable oxidation state of the element will be

Which of the following electronic configurations will have the least $I.P.$ value?