How many molecules are in 2.50 moles of so2

Every compound or element has a fixed number of molecules per mole. This is given by the Avogadros number which is about 6.022 x 10^23 molecules per mole. Therefore:

molecules = 2.50 moles * (6.022 x 10^23 molecules / mole)

molecules = 1.5055 x 10^24 molecules of SO2