In the chemical reaction shown hydrogen and oxygen are classified as reactants.
Reactants are substances that combines with each other to give a new substance(s) called products.
Reactants are always shown at the left hand side of a chemical reaction equation while products are shown at the right hand side of a reaction equation. Both sides are separated by the arrow.
Hydrogen and oxygen appeared at the left hand side in the equation; 2H2 + O2 → H2O, hence they are reactants.
Learn more: https://brainly.com/question/17096236