Which of the following dopants is added to silicon to obtain an $n$-type semiconductor?

Which of the following can act as a $p-$type semiconductor?

Define the term 'Isotropic' property.

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.

Match items of List-$I$ with those of List-$II$ :

List-$I$ (Property)	List-$II$ (Example)
$a$. Diamagnetism	$i$. $MnO$
$b$. Ferrimagnetism	$ii$. $O_{2}$
$c$. Paramagnetism	$iii$. $NaCl$
$d$. Antiferromagnetism	$iv$. $Fe_{3}O_{4}$

Choose the most appropriate answer from the options given below:

Which of the following possesses a layered crystal structure?