The position of three elements $A$,$B$ and $C$ in the Periodic Table are shown below:

Group $16$	Group $17$
-	-
-	$A$
-	-
$B$	$C$

$(a)$ Will $C$ be larger or smaller in size than $B$?
$(b)$ Which type of ion,cation or anion,will be formed by element $A$?

(N/A) will be smaller in size than $B$. As we move from left to right across a period,the nuclear charge increases,which pulls the electrons closer to the nucleus,resulting in a decrease in atomic size.
$(b)$ $A$ will form an anion. Since $A$ belongs to Group $17$,it has $7$ valence electrons and needs one more electron to complete its octet,thus it gains an electron to form a negatively charged ion (anion).