Rate of reaction $=[A]^a$
Order of reaction $= a$
$[A]_1 = 2.2 \,m\,M$, $r_1 = 2.4\, m\,M\,s^{-1}$ ... $(i)$
$[A]_2 = 2.2/2\, m\,M$, $r_1 = 0.6\,m\,M ^{-1} $ or, $\frac{{2.4}}{4}$ ..... $(ii)$
On reducing the concentration of $A$ to half, the rate of reaction is decreased by four times.
Rate of reaction $=[A]^2$
Order of reaction $= 2.$
${{H}_{2}}+C{{l}_{2}}\xrightarrow{\text{Sunlight}}2HCl$