• CrO₂ behaves like a metal also can conduct electricity. Because Cr is a transition metal and has d-electrons (electrons present in d-orbitals) which are partially filled and leads to electrical conductivity just like metals having free electrons.

(i) SiO₂ (quartz) is a network solid which is covalent in nature and always behave as an insulator ( no free electrons to conduct electricity).

And (ii) MgO is an ionic crystalline solid which means it acts as an insulator in the solid-state( as there is no free movement for ions) and conducts electricity in the molten or aqueous state(ions overcome electrostatic attractions and are free to move).

(iii) SO₂(s) is a polar molecular crystal and therefore is formed by stronger dipole-dipole interactions which make them non-conductors of electricity, unlike metals.