What are the mole ratios in the chemical equation H2+Cl2?
To complete your equation,
The mole ratios (fancy term is stoichiometry) are simply the numbers in front of each chemical formula which are used to balance the equation. In this case, the equation reads "one mole of hydrogen reacts with one mole of chlorine to make two moles of hydrogen chloride".
A common misconception is to think that because equations are supposed to be balanced, that there should always be the same number of moles on each side. This is NOT true! There have to be the same number of each type of atom on each side of the equation, but in order to make that work you often will end up with different numbers of moles on each side, which is not a problem.