Concept:The reaction goes to completion, so the number of moles of reactant equals the number of moles of product.Explanation:Molar mass of 4‑nitrotoluene is 137 gmol−1.Given mass is 137 mg, which is 0.137 g.Moles of 4‑nitrotoluene = 137 gmol−10.137 g​=0.001 mol.Moles of product B formed = 0.001 mol (1:1 ratio).Molar mass of B is 228 gmol−1.Mass of B = 0.001 mol×228 gmol−1=0.228 g.Convert to mg: 0.228 g=228 mg.