Answer: Option (d) is the correct answer.
Step-by-step explanation:
A change causes change in chemical composition of a substance is known as a chemical change.
For example, reactivity, toxicity, combustion etc are all chemical properties.
Chemical changes lead to the formation of new compounds. As a result, there occurs change in molecular structure of a compound.
Whereas a change that does not bring any changes in chemical composition of a substance is known as a physical change.
For example, boiling point, density, volume, melting point etc are all physical properties.
Thus, we can conclude that the molecular structure has changed is an indication that a substance has undergone a chemical change.