Which of the following statements is incorrect?

With which of the following electronic configurations does an atom have the lowest ionisation enthalpy?

The sum of $IE_1 + IE_2$ and $IE_3 + IE_4$ for elements $P$ and $Q$ are given below:

Element	$IE_1 + IE_2$ $(kJ/mol)$	$IE_3 + IE_4$ $(kJ/mol)$
$P$	$2.45$	$8.82$
$Q$	$2.85$	$6.11$

Then,according to the given information,the incorrect statement$(s)$ is/are:

If the first ionisation enthalpy of $Li$,$Be$,and $C$ respectively are $520$,$899$,and $1086 \ kJ \ mol^{-1}$,the first ionisation enthalpy (in $kJ \ mol^{-1}$) of $B$ will be:

Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

The successive ionization energy values for an element $X$ are given below:
$(i)$ $1^{st}$ ionization energy $= 410 \ kJ \ mol^{-1}$
$(ii)$ $2^{nd}$ ionization energy $= 820 \ kJ \ mol^{-1}$
$(iii)$ $3^{rd}$ ionization energy $= 1100 \ kJ \ mol^{-1}$
$(iv)$ $4^{th}$ ionization energy $= 1500 \ kJ \ mol^{-1}$
$(v)$ $5^{th}$ ionization energy $= 3200 \ kJ \ mol^{-1}$
Find the number of valence electrons in the atom $X$.