Asap. what is an example of a physical change? having less ash than the paper that was burned to form it.
ice forming and then melting back into water.
rust having a different identity than the iron it forms on.
the irreversible reaction of vinegar and baking soda.

This is what a calorimeter is used for simpler ex, to measure calories in food.

The best answer is (a) which is universal law is in effect at all times. it is constantly at play in everything we do and governs our lives. it is also important to note that universal law applies to not only everything on earth, but everything in the universe as well, which is another reason why it is in effect at all times.