Question

two oxides of an element contain 57.1% and 72.7% of oxygen. If the first oxide is MO the second is: (a) M2O (b) MO2(c) M2O2 (d) M2O3

Answer 1

In 1st oxide:
Amount of oxygen= 57.1 g
amount of M= 42.9g

In 2nd  oxide:
amount of oxygen= 113.45 g
amount of M= 42.9 g

as the amount of M is fixed the ratios of oxygen are 
56.1 : 113.45
1:2

so the formula of 2 oxides are MO and MO₂