Question

what are chemical reactions? when substances change into new ones with different properties by rearranging their atoms. the process of mixing substances together so they are evenly mixed. a method of separating mixtures into individual parts.

Explanation:

Chemical reactions involve substances changing into new substances with different properties by rearranging their atoms. Mixing substances evenly is just a physical - mixing process and separating mixtures is a physical separation process, not chemical reactions.

Answer:

The first option: When substances change into new ones with different properties by rearranging their atoms.