The molecular formula for ammonia is NH3. It is made out of one nitrogen molecule and three hydrogen molecules. Ammonia is a colorless gas and has a pungent smell. It is also lighter than air and easily liquefied due to the strong hydrogen bonding between molecules. The liquid boils at −33.3 °C and freezes to white crystals at −77.7 °C. It is important because it is the main factor in controlling algal growth when other nutrients are abundant. About 80% of the ammonia produced by industry is used in agriculture as fertilizer. It is also toxic and used as a refrigerant gas, for the purification of water supplies, and in the manufacture of plastics, explosives, textiles, pesticides, and dyes.