The question requires that you assume complete ionization of the compound. This is:
(NH4)2 SO4 → 2 NH4 (+) + SO4 (2-)
Then, 1 mol of (NH4)2 SO4 produces 3 moles of ions: 2 moles of NH4 (+) and 1 mol of SO4 (2-)
=> 0.26 * 2 moles of NH4(+) = 0.52 moles of NH4 (+)
0.26 * 1 mol of SO4 (2-) = 0.26 moles of SO4 (2-).
Answer: 0.52 moles of ammonium ions and 0.26 moles of sulfate.ions.
