Question

How many molecules of oxygen gas are in 1.42 moles of oxygen gas ?

Answer 1

You have 1.42mol O2.

If 1mol is 6.022*1023 molecules of O2, then 1.42mol O2 is equal to 1.42*6.022*1023 molecules of O2. This gives a total of approx. 8.55*1023 molecules of oxygen gas.