What do you understand by
(a) Allotropy `" "` (b) Inert pair effect ?

Explanation

`to` The phenomenon of existence of an element in different physical forms having similar (or) same chemical properties is called allotropy.
`to` Crystalline allotropes of carbon are a)-Diamond b) Graphite.
b)Inert pair effect. The reluctance of .ns pair of electrons to take part in bond formation is known as inert pair effect.
(or)
(or)The occurrence of oxidation states two units less than the group didation states is known as inert pair effect.
Eg: Lead exhibits+2 oxidation state as stable oxidation state due to inert pair effect. Instead of 14 state) .
Catenation : The phenomenon of self linkage of atoms among themselves to form long chains (or) rings is called as catenation.
`to` Carbon has highest catenation tendency due to its high bond energy (348 KI/mole).