Solid $CO_2$ is an example of

Quartz is a crystalline variety of

The reason why solid $NaCl$ is a poor conductor of electricity is .......

Which of the following statements is correct?

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

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.