Initial concentration Rate of reaction
$2\times 10^{-3}\,M$ $2.40\times 10^{-4}\,MS^{-1}$
$1\times 10^{-3}\,M$ $0.60\times 10^{-4}\,MS^{-1}$
rate of reaction
$r\,=\,k\,[A]^x$
where $x\,=$ order of reaction
hence
$2.40 \times {10^{ - 4}}\, = \,k\,{[2 \times {10^{ - 3}}]^x}$ ..... $(i)$
$0.60 \times {10^{ - 4}}\, = \,k\,{[1 \times {10^{ - 3}}]^x}$ ..... $(ii)$
on dividing eqn. $(i)$ from eqn. $(ii)$ we get
$4\,=\,(2)^x$
$\therefore \,\,x=2$
i.e., order of reaction $=2$