the answer
the number of moles can be found easily by using formula of molar mass
Molar mass = mass (g) / number of moles (mol)
from this, we can get number of
number of moles (mol) =mass (g) / Molar mass
the mass molar of (NH4)2S :
M((NH4)2S) = (14+ 4x1) x 2 + 32 = 36+32 = 48 g/ mol
number of moles (mol) = 150 g / 48 = 3.12 moles
