The starting material in a chemical reaction is called a reactant.
Reactants are the substances that are present at the beginning of a chemical reaction. During the reaction, they undergo a transformation to form new substances known as products. Understanding the role of reactants is crucial in the study of chemical reactions as it helps in predicting the outcome and efficiency of the reaction. For instance, in the combustion of hydrogen in oxygen, both hydrogen and oxygen serve as reactants, which react to produce water.