Consider the following reactions.
$$ \begin{array}{r} \mathrm{Cs}+\mathrm{O}_2 \text { (excess) } \rightarrow X \\ \mathrm{Na}+\mathrm{O}_2 \rightarrow Y \end{array} $$
Identify the correct Statement about $X$ and $Y$
Choose the correct statement from the following.
I. In vapour phase $\mathrm{BeCl}_2$ exists as chlorobridge dimer.
II. $\mathrm{BeSO}_4$ is readily soluble in water.
III. BeO is completely basic in nature.
IV. $\mathrm{BeCO}_3$ being unstable, is kept in the atmosphere of $\mathrm{CO}_2$.
V. $\mathrm{BeCO}_3$ is less soluble among all the carbonates of group 2 elements.
Observe the following reactions (not balanced)
$$ \begin{aligned} & \mathrm{BF}_3+\mathrm{LiAlH}_4 \xrightarrow{\left(\mathrm{C}_2 \mathrm{H}_5\right)_2 \mathrm{O}} X+\mathrm{LiF}+\mathrm{AlF}_3{ }^{-} \\ & X+\mathrm{NaH} \longrightarrow Y \end{aligned} $$
The incorrect statement about $Y$ is