Step 1 - What is a chemical reaction?
A reactin reaction is a transformation in which chemical bonds are broken. As a consequence, new substances are formed.
There is no chemical reaction without the breaking of chemical bonds, but there are of course such phenomena, which are thus called physical changes.
Step 2 - Analysing the alternatives
a) Only physical changes: no. As we saw, a chemical reaction involves the breaking of chemical bonds, while a physical changes does not.
b) New substances must form: yes. As a result of the breaking of bonds, new substances are produced
c) Only changes of state occur: no. These are physical changes.
d) Chemical properties remain the same: no.
Answer: b) New substances are formed
