An astronaut gets thirsty on the moon. So, he prepares water by mixing hydrogen and oxygen. Will the mass ratio of hydrogen to oxygen present in the water on moon will be same as that on the earth?
It will be the same.
According to 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 will be 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 that mass of oxygen is always 1:8 always whatever be the source of water. Water has to exist in the mass ratio of 1:8, whatever the method or the source from which it is obtained.