Which of the following reactions is not correct according to the law of conservation of mass ?
A. `2Mg(s)+O_(2)(g)rarr2MgO(s)`
B. `C_(3)H_(8)(g)+O_(2)(g)rarrCO_(2)(g)+H_(2)O(g)`
C. `P_(4)(s)+5O_(2)(g)rarrP_(4)O_(10)(s)`
D. `CH_(4)(g)+2O_(2)(g)rarrCO_(2)(g)+2H_(2)O(g)`