In compound 1.00g of nitrogen unites with 0.57g of oxygen. In compound B, 2.00g of nitrogen combines with 2.24g of oxygen. In compound C. 3.00g of nitrogen combines with 5.11g of oxygen. These results obey the following law

Here, According to the question

Compound A : 1.00 g N + 0.57 g O₂

Compound B : 2.00 g N + 2.24 g O₂

Compound C : 3.00 g N + 5.11 O₂

So If we fixed the amount of nitrogen (1 g) for all compound then,

Compound A :

1.00 g of N combine with  0.57 g of O₂

Compound B :

2 g N of N combine with 2.24 g of  O₂

1g N=1.12g O₂ 

Compound C :

3 g N combine with 5.11 O₂

1 g N = 1.70 g O₂

Thus, Take in consideration the ratio of oxygen of all three compounds for the fixed amount of Nitrogen, then we get, Ratio of oxygen ≈ 1 : 2 : 3
This ratio indicates the law of multiple proportion.