The correct answer is A. N2O, or nitrous oxide. It is a colorless, odorless gas that is used as an anesthetic and pain reliever. It is also known as laughing gas because it can cause people to laugh uncontrollably when they inhale it.
B. CO2, or carbon dioxide, is a colorless, odorless gas that is found in the air. It is also produced when animals breathe and when plants decompose. Carbon dioxide is used in fire extinguishers and in the production of carbonated beverages.
C. H2O, or water, is a colorless, odorless liquid that is essential for life. It is found in the oceans, lakes, rivers, and glaciers. Water is also used in many industrial processes.
D. SO2, or sulfur dioxide, is a colorless, odorless gas that is produced when sulfur is burned. It is also a byproduct of the burning of fossil fuels. Sulfur dioxide is a major contributor to acid rain.