Because you are never adding more than the substances created, nor are you creating any, but should a chemical reaction take place you could see the liquid change form into a gaseous state and that would result a loss of the liquid volume.
So to wrap it all up you can’t have more liquids than what is already there but you could always lose some due to a chemical change, hence the reason it says an open flask, the chemical change would not be collected, mass would be lost
Answer:
Mg would blow off. AI would be affective to copper but not to MG
Explanation:
Planck suggested that light/energy was absorbed/released in certain amounts, called quanta.
