According to the law of conservation of mass, the total mass of the reacting substances is

Question

$\begin{array}{1 1} \text{(a) always more than the total mass of the products} \\ \text{ (b) always less than the total mass of the products} \\ \text{ (c) sometimes more and sometimes less than the total mass of the products} \\ \text{ (d) always equal to the total mass of the products.} \end{array}$