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 one of the following elements, when present as an impurity in silicon, makes it a $p$-type semiconductor?

$A$ clock spring is heated to redness and then plunged into cold water. This treatment will cause it to become

Choose the correct option for crystalline solids based on the following statements:
$(1)$ They do not have a sharp melting point.
$(2)$ They gradually soften upon heating.
$(3)$ They have an irregular three-dimensional arrangement.
$(4)$ They show a rapid change in volume upon heating.

Solid methane is

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.