Question

1. total mass before and after a chemical reaction is the same

Explanation:

The first statement describes the Law of Conservation of Mass, which is a fundamental principle in Chemistry (a subfield of Natural Science). This law states that in a closed system, the total mass of substances before a chemical reaction is equal to the total mass of substances after the reaction, as atoms are neither created nor destroyed, only rearranged.

For the second statement, it seems to be cut off, but if we assume it's about a type of change in matter (e.g., "a change in matter in which..."), a chemical change involves a transformation where new substances are formed, while a physical change does not. If it's about the type of change related to the first statement (conservation of mass), chemical reactions (which involve chemical changes) follow the conservation of mass.

If the question is to identify the concept in the first statement:

The statement refers to the Law of Conservation of Mass, a key concept in Chemistry (Natural Science) stating mass is conserved in chemical reactions.

Answer:

Law of Conservation of Mass (related to Chemistry, Natural Science)