The reaction L-M is started with 10 g/L. After 30 and 90 minute, 5 g and 1.25 g/L are left respectively. The order of reaction is-a.2b.1

since in 30 minutes 10 gram degrees to 5 gram and in 60 minutes it decreases to 2.5 gram and then in 90 minutes to 1.25 gram...... hence we find a uniform decrease which is only in the case of a first order reaction just like the radioactive reactions which we know that radioactive reactions are of first order.. nhencef first order reaction