When magnesium is burnt it rects with the oxygen. This creates magnesium oxide. The oxygen also has mass so it makes sense that the two when combined will have a higher mass than the original magnesium on it's own.
Its also almost impossible to put out once it catches on fire. Even submerged into water it breaks the hydrogen and oxygen apart and keeps burning :D.
Cool Learn something every day :D.
well sed lol XD
