Identify the pair of hydrides which have polymeric structure

The proper conditions of storing $\mathrm{H}_{2} \mathrm{O}_{2}$ are

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

The dihedral angles in gaseous and solid phases of $\mathrm{H}_2 \mathrm{O}_2$ molecule respectively are

Consider the following statements about the hydrides. (I) Sodium hydride with water liberates oxygen gas. (II) Methane, silane are examples of electron precise hydrides. (III) Ammonia and water molecules are examples of electron deficient hydrides. (IV) Hydrides of beryllium and magnesium are polymeric in structure. The correct statements are

Match the following. The correct answer is