In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water. In the example reaction, two moles of hydrogen react with one mole of oxygen and produce two moles of water. By the way, Avogadro's Number is the factor between the two points above. Answer - when no coefficient is present, assume a one to be present. There are three important things to remember about reading an equation.
Reactants are on the left and products are on the right.
If no number is shown, a one is understood.