Question

Explain how a pile of ashes has the same mass as the original log before it was burned. What is the law that defines this

Answer 1

This is based on the Law of Conservation of Mass. The log is simply changed from a solid log, into gasses and ash. Mass is not added or removed, it is just changed.

Answer 2

that's law of conservation of mass..
the original log changes its form of mass that ash but the total mass of the system remains constant that's the law of conservation of mass