1)
Na3PO4 + H2SO4 => Na2SO4 + H3PO4
We must have the same number of atoms on both sides.
We start with Na,
2 Na3PO4 + H2SO4 =>3 Na2SO4 + H3PO4 (6 Na on both sides)
Then we proceed with P,
2 Na3PO4 + H2SO4 =>3 Na2SO4 +2 H3PO4 (2 P on both sides)
After that, we continue with S,
2 Na3PO4 + 3 H2SO4 =>3 Na2SO4 +2 H3PO4 (3 S)
The number of H and O are solved.
Answer: 2 Na3PO4 + 3 H2SO4 =>3 Na2SO4 +2 H3PO4