In this question, we have to do something different, since we now have the mass and not the number of moles of Hg2S, we need to find the number of moles and we will do that by using the molar mass of Hg2S, 232.66g/mol
232.66g = 1 mol
800g = x moles of Hg2S
x = 3.44 moles of Hg2S
Now we can use this number of moles and Avogadro's constant number
1 mol = 6.022*10^23
3.44 moles = x particles
x = 2.07*10^24 particles of Hg2S
