Answer:
Remain the same
Explanation:
The law of mass conservation states that matter cannot be created nor destroyed but can be converted from one form to another.
Essentially, what Lavoisier was trying to proof is that by heating the mixture, after all the change the mass still remains. That was why he used a sealed flask. If the flask was not sealed, it probably would have been that some of the mass will escape as vapor to the atmosphere which might be difficult to account for
