Answer:
= 4.9 x 10^25 molecules of SF6
Step-by-step explanation:
There's a guy named Avogadro something who said 1 mole of anything has 6.022x10^23 units (such as molecules, ions etc.) of that thing.
So to get to molecules just multiply 81 moles by 6.022x10^23
= 4.9 x 10^25 molecules of SF6