Which of the following have least number of atoms :

[tex](1) 5.6 l \: NH_{3}[/tex]

[tex](2) 4g \: O_{2}[/tex]
[tex](3) 3.01 × 10²² \: moles \: of H_{2} SO_{4}[/tex]
[tex](4) 2.24 g \: of \: H_{2} \: gas[/tex]
I want complete solution..​