Final answer:
The properties of substances change when they undergo a chemical reaction and form new substances. option c.
Step-by-step explanation:
The information provided supports option C: When substances are chemically combined, the properties of the new substances that are formed are often different from the properties of the original substances.
In the case of sodium and chlorine, their individual properties change drastically when they react with each other. Sodium is a highly reactive metal that reacts explosively with water, while chlorine is a poisonous gas. However, when they combine, they form sodium chloride, which is a harmless and essential compound known as table salt.
This clearly demonstrates that the properties of the substances change when they undergo a chemical reaction and form new substances with different properties.