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

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

$(a)$ State whether $A$ is a metal or non-metal.
$(b)$ State whether $C$ is more reactive or less reactive than $A$.

$A$ is a non-metal because it belongs to Group $17$, which consists of halogens, and all halogens are non-metals.
$(b)$ $C$ is less reactive than $A$. In Group $17$ (halogens), the reactivity of elements decreases as we move down the group because the atomic size increases and the tendency to gain an electron decreases.