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

50% of a reaction occurs in 100 second and 75% of the reaction occurs in 200 second, the order of this reaction is 1 .
Let the initial reactant concentration is $1\mathrm{M}$.
In first 100 seconds, reactant concentration is reduced to $50\%$ or $1\times \frac{50}{100}=$$0.5\mathrm{M}$

In second 100 seconds (total 200 seconds from start), reactant concentration is reduced to $100-75=25\%$ or $1\times \frac{25}{100}=0.25\mathrm{M}$.