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 $=2$