$XeF_4$ on partial hydrolysis produces

The noble gas that does not occur in the atmosphere is

The shape of $XeOF_4$ molecule is

Select the $INCORRECT$ statement regarding the following reactions:
$XeF_6 + \text{excess } H_2O \rightarrow 'X' + HF$
$XeF_6 + 2 \text{ moles } H_2O \rightarrow 'Y' + HF$

Explain the variations in the following properties of group $18$ elements:
$(i)$ Atomic radii
$(ii)$ Ionisation enthalpy
$(iii)$ Electron gain enthalpy

Assertion $(A)$: Helium has the lowest boiling point $(4.2 \ K)$.
Reason $(R)$: The forces that exist between helium atoms are weak dispersion forces.