How many hydrogen atoms are in 8.90 mol of ammonium sulfide?

Assuming that the ammonium sulfide formula is (NH4) 2 S then you can see that there are 2 nitrogen, 8 hydrogen and 2 sulfur atoms for every ammonium sulfide. If the amount of ammonium sulfide is 8.9 moles, then the number of hydrogen atoms should be: 8/1 * 8.9 mol = 71.2 moles.

If you are asked the number of individual atoms you need to multiply it with Avogadro number like this : 71.2 moles * 6.02 * 10^23 = 4.28 * 10^25