The formula for ammonium sulfide is (NH4)2S. Each ammonium ion, (NH4)^+, contains four hydrogen atoms. So 7.00 mol of ammonium sulfide contain:

$$7.00 \text{ mol (NH}_4)_2\text{S} \times \frac{8 \text{ mol H}}{1 \text{ mol (NH}_4)_2\text{S}} = \boxed{56 \text{ mol H}}$$