Which of the following possesses a layered crystal structure?

Which of the following substances is not ferromagnetic?

Solid $NaCl$ is a bad conductor of electricity since:

Crystals of which pair are isomorphous?

Doping of silicon $(Si)$ with boron $(B)$ leads to:

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.