If the arrangement of atoms in a substance changes, then which of the following is true? a. a chemical reaction has occurred. b. the physical state of the substance changes. c. the chemical properties of the substance stay the same but the physical properties change. d. the physical properties of the substance stay the same but the chemical properties change.

Option (a) is the correct answer.

Explanation:

A chemical reaction is defined as the reaction in which bonds between the reactants either break or form which leads to the formation of a new substance.

For example,

Here, lithium chloride formed is a new substance which occurred due to formation of chemical bond between the reactants, that is, lithium and chlorine.

As a result, chemical properties of both reactants and products will be different.  

Thus, we can conclude that the statement a chemical reaction has occurred, is true.

the answer is b i think