An astronaut gets thirsty on the moon. So, he makes water by mixing hydrogen and oxygen. Will the mass ratio of hydrogen to oxygen present in the water, he made on the moon, be the same as that on the earth?
It will be the same.
According to the Law of constant proportion, in a given chemical compound, the elements are always present in definite proportions by mass. So the mass ratio of the water remains the same irrespective of place.
For eg: The chemical formula of water is H2O, which means water requires only 2 molecules of hydrogen and 1 molecule of oxygen irrespective of its location. The ratio of mass of hydrogen to the mass of oxygen is always 1:8.