Solid $A$ is a very hard electrical insulator in solid as well as in molten state and melts at extremely high temperature. What type of solid is it?

Which among the following is $NOT$ an amorphous solid?

Classify solids based on their electrical conductivity.

Classify the following materials into superconductors,conductors,semiconductors,and insulators: $Cu$,$Al$,$Si$,$Ge$,glass,Teflon,$Au$,$Pt$,$CuO$ (at low temperature),graphite,carbon black,and alloys at low temperature.

Which of the following elements has the smallest energy gap?

The one that is extensively used as a piezoelectric material is