First member of each group of representative elements (i.e., s and p-block elements) shows anomalous behaviour. Illustrate with two examples.

Answer

A

Explanation

First member of each group of representative elements (i.e, s- and p-block elements) shows anomalous behaviour due to i) small size, ii) high ionisation enthalpy, iii) high electonegartivity and (iv) absence of d-orbitals e.g. in s-block elements, lithium shows anomalous behaviour from rest of the alkali metals.
a) Compounds of lithium have significant covalent character. While compounds of other alkali metals are predominantly ionic.
Lithium reacts with nitrogen to form lithium nitride while other alkali metals do not form nitrides.
In p-block elements, first member of each groups has four orbitals, one 2s-orbital and three 2p-orbitals it their valence shel.. So, these elements show a maximum covalency of four while othe member of the same group or different groups show a maximum covalency beyond four due to availability of vacant-d-orbitals.