What only happens during a chemical reaction?
a. a solution is made.
b. new substances are formed.
c. bubbles form.
d. colors change.

B. New substances are formed. In a chemical reaction, the starting molecule must be changed or turn into another. For example: rusts that form in a tin can is a chemical reaction. The iron in the can combines with the oxygen in the atmosphere, creating rust (iron oxide), which is a different substance.