1] Find out how many moles
2] Use Avagadro's number to find number of molecules
1] [2.3 g (NH4)2SO4] x [1 mol (NH4)2SO4] / [132.14g(NH4)2SO4 )] = 0.017406 moles (NH4)2SO4
2] 0.017406 moles x 6.022 x 10^23 molecules/mole = 1.05 x 10^21 molecules (NH4)2SO4