Exhaust gas is the mixture of gases produced when fuel is burned in an engine, such as in cars or airplanes. This gas is released into the atmosphere through the exhaust system, which includes components like the exhaust manifold and muffler. Common components of exhaust gas include carbon dioxide, water vapor, nitrogen oxides, and unburned hydrocarbons. The composition of exhaust gas can vary depending on the type of fuel used and the efficiency of the combustion process. Reducing harmful emissions from exhaust gas is important for environmental protection, leading to the development of technologies like catalytic converters and electric vehicles.