how many moles of sodium phosphate are required to make 7.5 moles of sodium nitrate in 2Na3PO4+3Be(NO3)=6NanO3+Be3(PO4)2

2.5 moles of sodium phosphate

Explanation:

3 Pb(NO3)2 + 2 Na3PO4 → Pb3(PO4)2 + 6 NaNO3

6 (moles in the reaction)- 7.5(moles  in the task)

2 (moles in the reaction)- x (moles in answer) ⇒6x = 2*7.5 ⇒ x = 15/6=2.5 (moles)