The correct answer is C. Reactants combine to form products
Step-by-step explanation:
A chemical reaction occurs as two or more substances interact, and this leads to the formation of new substances. In this context, the initial substances are known as reactants, while the substances at the end of the process are known as products. For example, by combining Carbon and Oxygen (reactants) you obtain Carbon Dioxide (Product) (C + O2 = CO2). Additionally, reactions can be of different types depending on the products obtained, this includes decomposition, synthesis and replacement reactions. According to this, the option that best describes a chemical reaction is "Reactants combine to form products".