Nitrogen gas is written as N2 and has two nitrogen atoms bonded together with a triple bond. It is the most abundant gas in the Earth's atmosphere (~80%). It is highly inert and unreactive to other chemicals. Chemists often use nitrogen gas to create an inert atmosphere for a chemical reaction in a reaction vessel. Due to this inertness, there is no true diagnostic test for nitrogen, but you can distinguish nitrogen from the other two most common atmospheric gasses (oxygen and carbon dioxide) with a couple of simple tests. If a flaming wooden splint or piece of paper is inserted into a tube of gas and the flame immediately goes out, then the gas is nitrogen versus oxygen (oxygen would feed the flame). If a wet piece of pH paper is inserted into a tube of gas and shows no change, then the gas is nitrogen versus carbon dioxide. Nitrogen is pH neutral while carbon dioxide is acidic in water and would turn the paper red.