Question

While burning paper a reduction in mass is observed. Is it an exception to the law of conservation of mass?

Answer 1

While burning paper we think that the mass has reduced. But the paper after burning reduces into ash, $C{O}_2$ and water vapour. $C{O}_2$ and water vapour being gaseous in state escapes into the environment leaving behind the ash. If we calculate the mass of ash, carbon dioxide and water vapour the total mass of the reactant and the product will remain the same thus verifying the law. Hence, it is not an exception as per law of conservation of mass.