What do you understand by $(a)$ inert pair effect,$(b)$ allotropy,and $(c)$ catenation?

(N/A) Inert pair effect: As one moves down the group,the tendency of $ns^2$ electrons to participate in chemical bonding decreases. This effect is known as the inert pair effect. In group $13$ to $16$ elements,the $ns^2$ electrons are held tightly by the nucleus due to poor shielding by $d$- and $f$-electrons,making them less available for bonding.
$(b)$ Allotropy: Allotropy is the existence of an element in more than one form,having the same chemical properties but different physical properties. The various forms of an element are called allotropes. For example,carbon exists in allotropic forms like diamond,graphite,and fullerenes.
$(c)$ Catenation: The ability of atoms of an element to link with one another through strong covalent bonds to form long chains or branched structures is known as catenation. It is most prominent in carbon and significant in $Si$ and $S$.