Question: How many ammonium ions NH4+ are there in 5.0 mol (NH4)2S?

Answer: 10 mol NH4+

Explanation:

In (NH4)2S, there are two ammonium ions (NH4+) for each formula unit of (NH4)2S. Therefore, 5.0 mol of (NH4)2S contains 5.0 mol x 2 = 10 mol of ammonium ions (NH4+).