Explain how do we classify materials as conductors and insulators on the basis of their resistance.

(N/A) Conductors are materials that possess a large number of free electrons $(\simeq 10^{28} \text{ m}^{-3})$ and exhibit very low resistivity $(\simeq 10^{-8} \Omega \text{ m})$. The resistivity of an ideal conductor is zero,and it increases with a rise in temperature in metals.
Insulators are substances that have practically no free electrons and possess very high resistivity $(\simeq 10^{16} \Omega \text{ m})$. The resistivity of an ideal insulator is infinity and decreases with a rise in temperature. Mica,rubber,glass,and porcelain are some examples of insulators.