CBSE Class 11-science Answered

This table shows the mass composition of some oxides of nitrogen

Now if we calculate the ratio of the masses of oxygen for the three oxides 2.28 : 1.14 : 0.57, it is equal to the ratio 4 : 2 : 1.  It means that if we have a fixed mass of nitrogen, the mass of oxygen which will combine with it cannot be just any amount or mass. There are only a few specific masses of oxygen which will combine with the fixed mass of nitrogen, and those specific masses are integer multiples of a fixed unit of mass.  The data in the table tell us that when we have a fixed amount of nitrogen, it can be combined only with some integer number of a fixed unit of mass of oxygen that means oxygen exists as fixed units of mass, or particles, and we call these particles "atoms" of oxygen.  Thus, the data in table lead us to a conclusion that the element oxygen is composed of individual atoms with identical mass.  We have shown that matter is made up of particles and that elements consist of identical particles or atoms.