: Rock salt, i.e., is anionic crystal. The lattice points in these crystals are occupied by positively and negatively charged ions. Each ion is surrounded by the largest possible no. of oppositely charged ions.

Quartz is a three-dimensional silicate, in which the repeating unit is and all four oxygen atoms are involved in sharing. It is also a covalent crystal. Diamond is a covalent crystal in which each carbon atom is hybridised and is covalently bonded to four other carbon atoms present at the four corners of a regular tetrahedron.

Dry ice is a molecular crystal wherein the lattice points are occupied by molecules which do not carry any charge. The binding energy in molecular crystals is weak owing to dipole-dipole attractions and van der Waals' forces.