In the second period of the long form of the periodic table,an element $X$ has the second lowest first ionization enthalpy and element $Y$ has the second highest first ionization enthalpy values. What are $X$ and $Y$?

Given below are two statements:
Statement $I$: The decrease in first ionization enthalpy from $B$ to $Al$ is much larger than that from $Al$ to $Ga$.
Statement $II$: The $d$ orbitals in $Ga$ are completely filled.
In the light of the above statements,choose the most appropriate answer from the options given below:

Match List-$I$ with List-$II$ with correct code:

List-$I$ ($IE_1, IE_2, IE_3$ in $kJ \ mol^{-1}$)	List-$II$ (Element)
$A$. $1510$	$1$. $H$
$B$. $495, 6500, 10200$	$2$. $Li$
$C$. $840, 1630, 13100$	$3$. $Be$
$D$. $600, 2050, 3100$	$4$. $B$

Outermost electronic configurations of four elements $A, B, C, D$ are given below:
$A: 3s^{2}$
$B: 3s^{2} 3p^{1}$
$C: 3s^{2} 3p^{3}$
$D: 3s^{2} 3p^{4}$
The correct order of first ionization enthalpy for them is:

The electronic configuration 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 $C$?

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