You are only allowed to ask one question at a time so I have edited down accordingly. Nitric oxide (NO) is a nitrogen double bonded to an oxygen. It exists as a radical, meaning the nitrogen has a single, unpaired electron associated with it. This means that the molecule is highly reactive to try to pair the single electron with an electron from another chemical. It is given off as a part of car exhaust and readily reacts with oxygen in the air to produce NO2, a component of smog. NO can be trapped in a solution of water with oxygen present to make nitrous acid (HNO2). The equation is given below.
4NO + O2 + 2H2O --> 4HNO2