Among the hydrides $\mathrm{NH}_3, \mathrm{PH}_3$ and $\mathrm{BiH}_3$, the hydride with highest boiling point is $X$ and the hydride with lowest boiling point is $Y$. What are $X$ and $Y$ respectively?

Xenon (VI) fluoride on complete hydrolysis gives an oxide of xenon ' $O$ '. The total number of $\sigma$ and $\pi$-bonds $\sin$ ' $O$ ' is i"

Consider the following reactions (not balanced).

$$ \begin{array}{r} \mathrm{BF}_3+\mathrm{NaH} \xrightarrow{450 \mathrm{~K}} X+\mathrm{NaF} \\ X+\mathrm{H}_2 \mathrm{O} \longrightarrow Y+\mathrm{H}_2 \uparrow \end{array} $$

The correct statements about $X$ and $Y$ are

I. $X$ is an electron deficient molecule.

II. in $X, B-B$ bond is present.

III. $Y$ is a weak tribasic acid.

IV. $Y$ acts as a Lewis acid.

Which of the following does not exist?