Answer : 2.31 moles of Helium was initially present in the balloon.
Explanation : Calculating the initial number of moles of helium in the balloon we need to use this method,
final moles present - 14.6 mol
Volume increased from 358.5 mL (= 0.3585 L ) to 2.26 L
(14.6 mol) x (0.3585 L / 2.26 L) = 14.6 moles X 0.158 L = 2.31 moles / L
Hence, the initial moles was 2.31 moles/L in the helium balloon.