Find the number of atoms present in 4.25g of NH3.

Molecular mass of ammonia= 14+3=17

In 1 molecule (nh3) there are 1+3=4 atoms

1 mole (17 g) has Avogadro number of molecules

17 g=> 1 mole

4.25g=>4.25/17=0.25 moles

1 mole = 4×6.022×10^23 atoms

0.25 or 1/4 mole =6.022×10^23 atoms.