What is ammonia oxidation?
Ammonia is (according to the World Book Millennium 2000) a colorless, soluble gas, consisting of one part nitrogen and three parts hydrogen, that has a very strong, pungent, and suffocating smell.
Let's start with the smell part: it doesn't take much ammonia to stink up the house, or the neighborhood! Ammonia is often contained in liquid household cleaners and it's used to make smelling salts. If you've ever gotten bonked in the head playing basketball or soccer and your coach puts a little white thing under your nose to get your attention - and it smelled terrible - that was ammonia!
As for ammonia being made up of nitrogen and hydrogen, think about water, or H2O. Water is made up of 2 parts hydrogen (H) and 1 part oxygen (O). So now you know that ammonia can be written as NH3, since it's made up of 1 part nitrogen (N) and 3 parts hydrogen (H).
BUT ...
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