The correct answer is A. H2SO4.
The COD test is a chemical test used to determine the amount of oxygen that is consumed by organic matter in a sample of water. The test is based on the principle that organic matter is oxidized by a strong oxidizing agent, such as potassium dichromate (K2Cr2O7), in the presence of an acid, such as sulfuric acid (H2SO4). The amount of oxygen consumed is then measured and used to calculate the COD of the sample.
The COD test is a widely used method for measuring the pollution levels in wastewater and sewage. It is also used to monitor the effectiveness of wastewater treatment plants.
The other options are incorrect because they are not strong oxidizing agents. HNO3 is nitric acid, HCl is hydrochloric acid, and none of these acids are strong enough to oxidize organic matter in the presence of K2Cr2O7.