Copper oxide was prepared by two different methods. In case one, 1.75 g of the metal gave 2.19 g of the oxide. In the second case, 1.14 g of the metal gave 1.43 g of the oxide. This is explained by which of the following laws?

The correct option is A Law of definite proportions
In case I,
mass of copper = 1.75 g
mass of copper oxide = 2.19 g
% of copper in the oxide =
$\frac{massofcopper}{massofcopperoxide}\times 100=\frac{1.75}{2.19}\times 100$
% copper = 79.9%
% of oxygen = 100 - 79.9 = 20.1%
In Case II,
mass of copper = 1.14 g
mass of copper oxide = 1.43 g
% of copper in the oxide =
$\frac{1.14}{1.43}\times 100$ = 79.7%
% of oxygen = 100- 79.7 = 20.3%
Thus copper oxide prepared by any of the given methods contain copper and oxygen in the same proportion by mass. Hence, it proves law of definite proportions.