Not all matter in the reactant goes to the product. Some matter is byproducts.
Is there any balanced equation near the question??
Answer:
103.7 grams
Explanation:

Al: 1 * 26.98 = 26.98
O: 2 * 16.00 = 32.00
H: 2 * 1.01 = 2.02
26.98 + 32.00 + 2.02 = 61.00
*
= 103.7 grams of 
K2 SO4 = 2[K+] + [SO4 2-]
Which means that every mol of K2SO4 gives 3 moles of ions.
Then 1.25 mol of K2SO4 gives 3*1.25 = 3.75 moles of ions.
Answer: 3.75