In which molecule is the van der Waals force likely to be the most important factor in determining the melting point $(m.pt.)$ and boiling point $(b.pt.)$?

If the value of ionic radius ratio $\left( \frac{r_c}{r_a} \right)$ is $0.52$ in an ionic compound,the geometrical arrangement of ions in the crystal is:

In silicon dioxide $(SiO_2)$,what is the structural arrangement of atoms?

The relative strength of interionic/ intermolecular forces in decreasing order is:

Which of the following substances is not a covalent solid?

The lattice enthalpy of an ionic compound is the enthalpy change when one mole of an ionic compound in its solid state dissociates into its ions in the gaseous state. It is impossible to determine it directly by experiment. Suggest and explain an indirect method to measure the lattice enthalpy of $NaCl_{(s)}$.