Bravo !

The question is referring to 1 mole of oxygen gas, which exist as only molecules.

So, 1 mole of oxygen molecules
= 6.02 x 1023 oxygen molecules

But the question is asking for the number of oxygen atoms. In each oxygen molecule, there are 2 oxygen atoms.

1 molecule 2 atoms

So, in 6.02 x 1023 oxygen molecules, there will be
(6.02 x 1023) x 2
= 12.04 x 1023
= 1.204 x 1024 oxygen atoms

6.02 x 1023 molecules ( 6.02 x 1023) x 2 atoms