How many moles of oxygen atoms are present in 3 moles of sulfur dioxide?

There are two moles of oxygen in one mole of sulfur dioxide, hence the molecular formula being SO2. Therefore, the number of oxygen moles will be double the number of moles of sulfur dioxide.

3 moles SO2 * (2 moles O) / (1 mole SO2) = 6 moles Oxygen atoms