Yes, a compound has a fixed composition. A compound is a substance that contains two or more elements chemically combined in fixed proportions by mass. This means that the ratio of the masses of the elements in a compound is always the same. For example, water is a compound that contains hydrogen and oxygen in a fixed ratio of 2:1 by mass. This means that for every 2 grams of hydrogen in water, there is always 1 gram of oxygen.