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

(N/A) The 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 electronegativity,and $(iv)$ absence of $d$-orbitals in the valence shell.
Examples:
$1$. In $s$-block elements,$Li$ shows anomalous behaviour compared to other alkali metals:
$(a)$ Compounds of $Li$ have significant covalent character,whereas compounds of other alkali metals are predominantly ionic.
$(b)$ $Li$ reacts with $N_2$ to form $Li_3N$,while other alkali metals do not form nitrides directly.
$2$. In $p$-block elements,the first member of each group has only four valence orbitals ($2s$ and $2p$). Consequently,these elements show a maximum covalency of $4$,whereas other members of the same group can show a covalency beyond $4$ due to the availability of vacant $d$-orbitals.