Assertion:  ${\mathrm{D}}_2\mathrm{O}$ is called heavy water.

Reason : Its degree of dissociation is high.

Assertion : ${\mathrm{H}}_2{\mathrm{O}}_2$ has higher boiling point than water.

Reason : The dipole moment of ${\mathrm{H}}_2{\mathrm{O}}_2$ is little more than that of ${\mathrm{H}}_2\mathrm{O}$.

Assertion : Beryllium hydride is a covalent hydride.

Reason : The electronegativity difference between $\mathrm{Be}$ and $\mathrm{H}$ is very high.

Assertion : The $\mathrm{O}-\mathrm{O}$ bond length of ${\mathrm{H}}_2{\mathrm{O}}_2$ is shorter than that of ${\mathrm{O}}_2{\mathrm{F}}_2.$

Reason : ${\mathrm{H}}_2{\mathrm{O}}_2$ is an ionic compound.