In which of the following the width of the forbidden zone between valance and conduction band is very big?

Insulators

The answer is 2. Insulators.

The forbidden zone is the energy gap between the valence band and the conduction band. In insulators, the forbidden zone is very wide, so it is difficult for electrons to jump from the valence band to the conduction band. This is why insulators do not conduct electricity well.

In conductors, the forbidden zone is very small, so it is easy for electrons to jump from the valence band to the conduction band. This is why conductors conduct electricity well.

Semiconductors have a forbidden zone that is intermediate between insulators and conductors. The forbidden zone in semiconductors can be narrowed by doping, which is the process of adding impurities to the semiconductor. Doping can make semiconductors more conductive.

Superconductors are materials that conduct electricity with zero resistance. The forbidden zone in superconductors is zero, so electrons can move freely from the valence band to the conduction band.

Here is a table summarizing the forbidden zone in different types of materials: