Answer:
By measuring the total mass of the matter before as well as after any physical or chemical change.
Step-by-step explanation:
As mentioned, according to the law of conservation of matter, no atoms can be created or destroyed when under physical or chemical change.
Naturally, all the matters have some mass associated with it.
To verify the law of conservation of matter, at first, measure the mass of matter before it underwent any physical or chemical change. Then, again, measure the mass of the matter after the physical or chemical change.
Now, observe both the mass, both must be equal. This verifies the law of conservation of matter.