Question

how many O2 atoms are present in 2.50 moles of 02 atoms
''       ''        ''     ''       ''      ''            '' ''        ''      '' 02 molecules

Answer 1

1.51E24 atoms of oxygen are present in 2.50 moles and 3.01E24 atoms of 2.50 moles are present.

Answer 2

1 mole=6.023*10^23 atoms or molecules
2.5 moles=2.5*6.023*10^23 
                =15.0575*10^23 atoms or molecules
=>15.0575*10^23 atoms or molecules are present in 2.5 moles of O2.