When elements are combined to form compounds, they undergo chemical change in which the properties of the composing elements are always different from the compounds formed after reaction. The change is not only applicable to the chemical properties of the elements but also the physical states of the substances. Answer then is B.
For examle, balanced chemical reaction of forming water from hydrogen and oxygen:
2H₂ + O₂ → 2H₂O.
During chemical reaction no particles are created or destroyed, the atoms are simply rearranged from the reactants to the products.
Oxygen (element) has boiling point of -183°C and hydrogen has boiling point of -253°C. In this chemical change water (compound) is produced and it has new boiling point, boiling point of water is 100°C.
The sum of the masses of potassium and iodine equals the mass of the product, potassium iodide. The results are consistent with he law of conservation of mass.
