The reaction $$L \to M$$  is started with $$10.0\,g$$  of $$L.$$  After 30 and 90 minutes $$5.0\,g$$  and $$1.25\,g$$  of $$L$$  respectively are left. The order of the reaction is

Solution :
After every 30 minutes the amount is reduced to $$\frac{1}{2}$$  therefore $${t_{\frac{1}{2}}}$$  is 30 minutes. In 90 minutes the amount is reduced to $$\frac{1}{8}$$  i.e. $$\frac{1}{{{2^n}}}.$$  Here $$n = 3.$$  True for 1^st order reaction.