(i) \(\mathrm{BeH}_2\) is a covalent hydride, therefore, it does not conduct electricity at all. \(\mathrm{CaH}_2\) conduct electricity in the fused state while \(\mathrm{TiH}_2\) conduct electricity at room temperature. Thus, the order of increasing electrical conductance is: \(\mathrm{BeH}_2 < \mathrm{CaH}_2 < \mathrm{TiH}_2\).
(ii) Electronegativity decreases down the group from \(\mathrm{Li}\) to Cs, therefore, the ionic character of their hydrides also increases in the same order, i. e., \(\mathrm{LiH} < \mathrm{NaH} < \mathrm{CsH}\).
(iii) Due to smaller size of \(\mathrm{D}\) as compared to \(\mathrm{H}, \mathrm{D}\)-D bond has the highest bond dissociation enthalpy followed by \(\mathrm{H}-\mathrm{H}\). However, due to repulsions between lone pairs of \(\mathrm{F}\) and the bond pair, F-F bond dissociation enthalpy is the minimum. Thus the bond dissociation enthalpy increases in the order:
\(\mathrm{F}-\mathrm{F} < \mathrm{H}-\mathrm{H} < \mathrm{D}-\mathrm{D} \text {. }\)
(iv) Ionic hydrides are powerful reducing agents. Both \(\mathrm{MgH}_2\) and \(\mathrm{H}_2 \mathrm{O}\) are covalent hydrides but the bond dissociation energy of \(\mathrm{H}_2 \mathrm{O}\) is much higher than that of \(\mathrm{MgH}_2\). Therefore, the reducing character increases in the order: \(\mathrm{H}_2 \mathrm{O} < \mathrm{MgH}_2 < \mathrm{NaH}\)