Silicon is

Among the following,which crystal will be soft and have a low melting point?

For amorphous solids,select the correct option using $T$ (True) or $F$ (False) for the following statements:
$(1)$ They soften over a range of temperature.
$(2)$ Their physical properties like electrical conductivity and thermal conductivity are the same in all directions.
$(3)$ The arrangement of their particles is disordered.
$(4)$ They are hard and are less affected by pressure.

An ionic solid is a poor conductor of electricity because ..........

Under which situations can an amorphous substance change to crystalline form?

Which of the following exists as covalent crystals in the solid state?