Nitrogen is a chemical element (atomic number 7).  At normal pressures and temperatures, it is a colorless, odorless gas.  It makes up about 75% of air. Unlike oxygen, nitrogen is not very reactive at normal temperatures and pressures, although it is found in many chemical compounds.  In organic chemistry, it is found in all proteins and in urea.  Most life forms cannot process gaseous nitrogen and must obtain it from other sources.  Animals get it from proteins found in plants and other animals, while plants usually have to get it from nitrogen compounds in the soil (including animal urine and feces).  However, legumes (most notably soybeans and peanuts) are capable of processing atmospheric nitrogen into chemical compounds and are rich in protein as a result.  

Liquid nitrogen is the gas of choice for cryosurgery due to the fact it won't react with human tissues, oxygen, surgical instruments or flammable objects.  

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