The correct option is (b) Flue gas
Easiest explanation: The products of combustion are in form of flue gas. Flue gas is the gas which is exiting to the atmosphere via a flue, which is channel for releasing exhaust gas from steam power plant. The flue gas is high in the contamination of nitrogen, oxygen and carbon dioxide. And also it contains a small amount of pollutants, such as soot and other types of oxides.