When a metal is burned in a closed container, the mass of the container and its contents do not change. a. observation. b. law. c. theory.

Answer: Option (b) is the correct answer.

Explanation:

According to the law of conservation of mass, mass of a substance can neither be created nor it can be destroyed but it can simply be transformed from one form to another.

Therefore, when a metal is burned in a closed container, the mass of the container and its contents do not change because they follows law of conservation of mass.

Thus, we can conclude that when a metal is burned in a closed container, the mass of the container and its contents do not change then it is a law.