What do you understand by (a) Inert pair effect (b) allotropy, (c) catenation

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#1

Inert pair effect: The heavier elements of groups
13,14,15 show an oxidation state two less than the number of valence electrons they possess.

The last element of these groups Tl, Pb, Bi
prefer to show oxidation states of + 1, + 2,
+ 3 in preference over + 3, + 4, + 5 which the ele-
ments of these groups normally exhibit. This is due
to the fact that as we go down in these groups, the
2 electrons of ns2 prefer to remain paired and do
not partidpate in bond formation. Such a pair of
electrons in called inert pair and the effect is called
the Inert Pair Effect.
(b) Allotropy : When an element exists in two or
more different forms, it is said to exhibit allotropy
and the different forms are called allotropes. For
example, phosphorous occurs in three allotropic forms, i.e., white, red and black. Sulphur shows
two different solid forms : Sulphur rhombic and
sulphur monochlinic.
© Catenation: Property of self-linking of atoms of
the same element through strong covalent bonds is
called catenation, e.g., C-C bonds in hydrocarbons,
It is due to strong C-C covalent bonds that catena-