Taking $\mathrm{NaCl}$ as an ionic compound, ${\mathrm{CCl}}_4$ as a covalent compound give four differences between ionic and covalent compounds.

Give the structure of Hydronium ion.

Element $\mathrm{X}$ is a metal with valency $2$, element $\mathrm{Y}$ is a non-metal with a valency $3$.

Write equations to show how $\mathrm{X}$ and $\mathrm{Y}$ form ions.