The following table shows elements represented by the letters $A, B, C, D, E, F, G$ and $H$.

Group	$1$	$2$	$13$	$14$	$15$	$16$	$17$	$18$
Element	$A$	$B$	$C$	$D$	$E$	$F$	$G$	$H$

$(i)$ Which of the elements has the atomic size:
$(a)$ biggest and $(b)$ smallest?
$(ii)$ Which element has valency:
$(a)$ $3$ and $(b)$ zero?

(A) $(i)$ Atomic size decreases across a period from left to right. Therefore,the element on the extreme left $(A)$ has the biggest atomic size,and the element on the extreme right (excluding noble gases,but here $G$ is in group $17$) has the smallest atomic size.
$(a)$ Biggest: $A$
$(b)$ Smallest: $G$
$(ii)$ Valency is determined by the number of valence electrons. Elements in group $13$ have $3$ valence electrons (valency $3$). Elements in group $18$ are noble gases with a stable octet (valency $0$).
$(a)$ Valency $3$: $C$
$(b)$ Valency $0$: $H$