H3PO4 is a tribasic acid and one of its salt is NaH2PO4.what volume of 1M NaOH solution should be added to 12g of NaH2PO4 to convert it into Na3PO4?

Answer 1

NaH2PO4 + 2NaOH ==> Na3PO4 + 2H2O

mols NaH2PO4 = grams/molar mass = ?
Use the coefficients in the balanced equation to convert mols NaH2PO4 to mols NaOH used.

Then M NaOH = mols NaOH/L NaOH. You know mols NaOH and M NaOH, solve for L NaOH. Convert to mL if that is the unit you want.