HNO2, or nitrous acid, is a weak acid that is typically found in aqueous solution. It is formed when nitrogen dioxide (NO2) dissolves in water. HNO2 is known for its role in various chemical reactions, including the production of nitrites, which are used in food preservation and as intermediates in organic synthesis. In its pure form, HNO2 is unstable and can decompose into nitrogen oxides and water. It is important in the field of chemistry for its applications in the synthesis of other compounds and its use in analytical chemistry. Safety precautions are necessary when handling HNO2 due to its corrosive nature.