NH4NO3 is called Ammonium nitrate. It is a type of salt. A salt is a product of the reaction of an acid and a base. For NH4NO3, it is a reaction of a weak base and a strong acid. The chemical equation for the formation of NH4NO3 can be written as:

NH4NO3 (aq) ---> NH4+  + NO3-

NH4+ is a conjugate acid of the weak base NH3. It is produced in the dissociation of NH3 in water.

NH3 (aq) + H2O  <----->   NH4+     +    OH-

NO3- is the conjugate base of the strong acid HNO3. It is produced from the dissociation of HNO# in water.

HNO3 + H2O     --->    H3O+   +  NO3-