Which equation obeys the law of conservation of mass? h2(g) + o2(g) → h2o(g) h2(g) + o2(g) → h2o(g) +4he(g) 2h2(g) + o2(g) → 2h2o(g) h2(g) → h2o(g) h2(g) + o2(g) → 2h2o(g)

The answer for #3 is c but i don't know why

12. complete each of the following word equations for synthesis reactions. a. sodium + oxygen -> b. magnesium + fluorine -> 13. complete and balance the equations for the decomposition reactions. a. hgo -> [with the triangle heat symbol above the arrow] b. h2o(l) -> [with "electricity" written above the arrow]

Which actions would increase the rate at salt dissolves in water? stir the water? crush the salt? use less water? heat the water? cool the salt