The students study the equations for the reactions of Na and Mg with H2O to explain the outcomes of the reactions. Which observation would provide the best evidence that matter is conserved in the reaction of Na and H2O?

A The number of atoms of Na is the same on both sides of the equation.

B The number of electrons and protons in Na is equal to the number of electrons and protons in H and O.

C The mass of Na and H2O that reacts is greater than the mass of H2 produced.

D The mass of NaOH produced is equal to the mass of H2O that is changed into steam as the Na explodes into flames.