Final answer:
In a double replacement reaction, the cations and anions switch partners. In this particular reaction, the products are Be(OH)2 and NH4SO4.
Step-by-step explanation:
In a double replacement reaction, the cations and anions in the reactants switch partners to form new compounds.
Based on the given reaction (BeSO4) + 2NH4OH -> Be(OH)2 + 2NH4SO4), the products will be Be(OH)2 and NH4SO4.