Answer is nitrogen trioxide.
NO3 is Nitrogen trioxide is blue liquid having unpleasant odour. It has low boiling point 3.5°C and held as a liquid by compression. It is an oxidizing agent, non-flammable but may cause fires when mixed with combustible materials. Reacts with reducing agents to generate heat. It is strong irritant to skin, eyes and mucous membranes. Its vapor is toxic if inhaled. It is used in special purpose fuels.