Question

how many nitrogen atoms are present in 160 amu of ammonium nitrate

Answer 1

In 180 amu of NH4NO3 there are 2mol of NH4NO3 and so there are 4 mol of Nitrogen atoms. 
Avogadro Constant tells us there are 6.022x10^23 particles per mol, so total number of N atoms = 2.4088x10^24

Answer 2

Explanation:Ammonium Nitrate is NH₄NO₃.The mass number of this molecule is 80 amu.So, in 160 amu of this compound, there are 2 (160/80) molecules.One molecule have 2 Nitrogen atoms.Therefore in 2 molecules (160 amu) there are 4 Nitrogen atoms.