Which among the following solids is a non-polar solid?

Which one of the following elements on doping with germanium, makes it a $p$-type semiconductor?

Select the correct statements.
$(A)$ Crystalline solids have long range order.
$(B)$ Crystalline solids are isotropic.
$(C)$ Amorphous solids are sometimes called pseudo solids.
$(D)$ Amorphous solids soften over a range of temperature.
$(E)$ Amorphous solids have a definite heat of fusion.
Choose the most appropriate answer from the options given below:

Explain doping.

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

What are unit cells? State its types. Enlist the characteristics of unit cell. Explain different types of unit cells.