In $n$-type semiconductors,the conduction of electricity is primarily due to which of the following?

Assertion : On heating ferromagnetic or ferrimagnetic substances,they become paramagnetic.
Reason : The electrons change their spin on heating.

Which forms a crystal of $NaCl$?

Which of the following statements is $NOT$ true regarding a crystalline solid?

$A$ pure crystalline substance,on being heated gradually,first forms a turbid-looking liquid and then the turbidity completely disappears. This behaviour is the characteristic of substances forming

Which of the following substances is a molecular solid?