Two gaseous samples were analyzed. One contained 1.2g of carbon and 3.2g of oxygen.  The other contained 27.3% carbon and 72.7% oxygen. The experimental data are in accordance with

% of carbon from 1st sample = $\frac{1.2}{1.2+3.2}\times 100=27.3$

% of oxygen from 1st sample = $\frac{3.2}{1.2+3.2}\times 100=72.7$

% of carbon and oxygen from both samples are same.

Above data confirms that both samples have same composition 

Therefore, law of definite proportions is obeyed.