Answer:
3.0580 moles are in 68.5 liters of oxygen gas at STP
Step-by-step explanation:
Let the number of moles of oxygen gas be n
Volume occupied by n moles of oxygen gas at STP = 68.5 L
At STP, 1 mol of gas occupies 22.4 L
Then 68.4 L of volume will be occupied by:

3.0580 moles are in 68.5 liters of oxygen gas at STP