+ The way you phrased this question makes it difficult to answer. To give an understandable answer, I need to know: what the reactants are, the amount of reactants, the purity of the reactants, and the temperature and pressure conditions. From what you’ve given I can tell that exactly 25% of the product will be emitted as gas, liquid or precipitate, probably all waste. The advantage is that, IF rigorous laboratory procedures are followed with SKILLS, almost 100% of your expected 75% yield should be NO2.