Which of the following isoelectronic ions has the lowest ionization energy?

Which of the following elements are at the peaks of the ionization energy trend?

For one of the elements,various successive ionization enthalpies (in $kJ \cdot mol^{-1}$) are given below:

$I.E.$	$1^{st}$	$2^{nd}$	$3^{rd}$	$4^{th}$	$5^{th}$
Value	$577.5$	$1810$	$2750$	$11580$	$14820$

The element is:

Elements $X, Y$ and $Z$ have atomic numbers $19, 37$ and $55$ respectively. Which of the following statements is true about them?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ The energy required to form $Mg^{2+}$ from $Mg$ is much higher than that required to produce $Mg^{+}$.
Reason $R:$ $Mg^{2+}$ is a small ion and carries more charge than $Mg^{+}$.
In the light of the above statements,choose the correct answer from the options given below:

The correct increasing order of ionisation enthalpy of $He, Li^{+}, Be^{2+}$ is