Aballoon contains 1.00 mol helium gas at stp. what will the volume of the balloon be if the pressure increases to 2.00 atm?

One mole of an ideal gas will occupy 22.4 liters of volume at STP.
If the only thing that changes is the pressure from 1.00 atm to 2.00 atm, then we know the initial volume, initial pressure, and final pressure. We can use Boyle's law.
Boyle's law: (initial pressure)*(initial volume) = (final pressure)*(final volume)
fill in the knowns
(1.00 atm)*(22.4 liters) = (2.00 atm)(final volume)
divide both sides by 2.00 atm
11.2 liters = final volume