If 50% of a reaction occurs in 100 seconds and 75% of the reaction occurs in 200 seconds, the order of this reaction is

t_1/2=100 seconds (50% reaction). After 200 seconds, 75% of reaction will be completed. i.e,. t_75% = 200 seconds. Thus it follows first order kinetics as half-life is independent of concentration and follows the relation ${\mathrm{t}}_{3/2}=2\times \mathrm{t}\frac{1}{2}$