what is the acid that is used to make ammonium nitrate???
Answers to questions of this kind are usually found readily by googling the key words.
For example, googling "ammonium nitrate" will give you a whole lot of information about the salt, how it's formed, the manufacturing processes, its applications/uses, etc.
You can also find lots of useful information here:
https://en.wikipedia.org/wiki/Ammonium_nitrate