Answer:
61.5%.
Step-by-step explanation:
We usually define percentage yield in chemistry as follows;
Percentage yield= actual yield/theoretical yield ×100
In this case we have;
Actual yield of the guaifenesin 400mg
Theoretical yield of the guaifenesin 650 mg
Hence;
Percentage yield of the guaifenesin =
400/650 ×100 = 61.5%
Hence the theoretical yield of the guaifenesin is 61.5%.