Which group of elements are all gases under normal conditions?

$XeF_6$ on partial hydrolysis with water produces a compound '$X$'. The same compound '$X$' is formed when $XeF_6$ reacts with silica. The compound '$X$' is

$XeF_6$ on partial hydrolysis gives

The correct decreasing order of the following $Xe$ compounds to act as both fluorinating and oxidizing agent is
$(I)$ $XeF_6$
$(II)$ $XeF_4$
$(III)$ $XeF_2$

Which one of the following statements regarding helium is incorrect?

Give the formula and describe the structure of a noble gas species which is isostructural with:
$(i)$ $ICl_{4}^{-}$
$(ii)$ $IBr_{2}^{-}$
$(iii)$ $BrO_{3}^{-}$