Which will be chemically more reactive: element $A$ with atomic number $17$ or element $B$ with atomic number $16$? Give a reason as well.

(A) $(i)$ Element $A$ (Chlorine) has an atomic number of $17$,and its electronic configuration is $(2, 8, 7)$. It needs to gain $1$ electron to complete its octet.
$(ii)$ Element $B$ (Sulfur) has an atomic number of $16$,and its electronic configuration is $(2, 8, 6)$. It needs to gain $2$ electrons to complete its octet.
$(iii)$ Reactivity in non-metals is determined by the ease of gaining electrons. Since element $A$ requires only $1$ electron to achieve a stable noble gas configuration,it is more chemically reactive than element $B$,which requires $2$ electrons.