Is it true that a chemical property is a property that can be measured or observed only when matter undergoes a change to become an entirely different kind of matter

No, not really.

Explanation:

A chemical property cant be said to have taken place by mere seeing and touching the object.

In other words, a chemical property of a substance can be defined as a quality obtained by changing the substance to a new identity, both physically and within the internal structures. So the internal structures of the substance must be investigated to affirm a chemical change.

answer; /// i believe the correct answer is (reactants);