Answer:
3.43Ă10š mol
Explanation:
Given data:
Initial number of  moles = 12.4 mol
Initial volume = 122.8 L
Final number of moles = ?
Final volume = 339.2 L
Solution:
The number of moles and volume are directly proportional to each other at same temperature and pressure.
Vâ/nâ Â = Â Vâ/nâ
122.8 L/ 12.4 mol  =  339.2 L / nâ
nâ = 339.2 LĂ 12.4 mol  / 122.8 L
nâ = 4206.08 L.mol /122.8 L
nâ = 34.3mol
In scientific notation:
3.43Ă10š mol