Why is it necessary to find the percent yield of a reaction?
a) to determine the efficiency of the reaction
b) to determine the amount of reactants in the reaction
c) to determine the amount of products in the reaction
d) to determine the limiting reactant of the reaction

The percent yield of a reaction is calculated in this way:

Percent yield = [Actual yield / theoretical yield] * 100

To calculate theoretical yield you need to know the number of moles that may react and that calculation starts with the limiting reagent, which is the reagent that is completely consumed as per the stoichiometry of the reaction.

So, the answer is the option D) to determine the limiting reactant of the reaction.

B. a graduated substance