To calculate the percentage yield of a chemical reaction, you can use the following formula:Percentage Yield = Actual Yield / Theoretical Yield x 100In this case, the actual yield is 12 grams, and the theoretical yield is 15 grams. Plugging these values into the formula:Percentage Yield = 12 grams / 15 grams x 100 = 0.8 x 100 = 80%So, the percentage yield of the chemical reaction is 80%.