Molar ratio is widely used in stoichiometry and it represents the number of moles of a compound needed to react with another compound in order to produce a specific amount of product, as the reaction we have in the question:
2 H3PO4 + 3 FeBr2 -> 6 HBr + Fe3(PO4)2
If we have H3PO4 as the focus, we will have the following molar ratios:
2 H3PO4 = 3 FeBr2
2 H3PO4 = 6 HBr
2 H3PO4 = 1 Fe3(PO4)2
These are the specific amounts of reactants needed and products produced in order for the reaction to occur
Therefore the answer is letter B, since 2 H3PO4 = 2 H3PO4 is not a correct molar ratio