How many atoms are in 3.690 moles of oxygen

1 mole of any substance contains Avogadro's number.

So, 1 mole of O2 = 6.023x10^23 molecules

3 mole of O2 = 6.023x10^23x3 molecules

= 1.8069x10^24 molecules

Each molecule of Oxygen has 2 atoms.

therefore,

1.8069x10^24 molecules = 1.8069x10^24 x 2 atoms

= 3.6138x10^24 atoms.