To answer this item, we are to assume that the given gas behaves ideally such that it can follow one of the simplified ideal gas law as written below,
P₁V₁ = P₂V₂
where P is the pressure and V is the volume.
Substituting the known values, while V₂ is unknown,
(100 atm)(10 L) = (1 atm)(V₂)
The value of V₂ is calculated to be equal to 1000 L.
The number of balloons that can be filled is as calculated.
n = (1000 L) / (1 L / balloon)
n = 1000