The initial rates for gaseous reaction $\mathrm{A}+3\mathrm{B}\to {\mathrm{AB}}_3 \mathrm{are} \mathrm{given} \mathrm{below}$

order of reaction is

With respect to A, no change in the rate if the concentration of A is doubled. So the order of ‘A’ is zero.

With respect to B, change in the rate becomes four times $\left(2^2\right)=\frac{0.008}{0.002}=4$if the concentration of B is doubled.

Hence $\mathrm{r}=\mathrm{K}{\left[\mathrm{A}\right]}^0{\left[\mathrm{B}\right]}^2$

Therefore, total order of reaction is 0+2=2