Answer:
Second option. 3
Explanation:
In order to balance a equation you need to have the same amount of atoms/moles in both sides.
Na₃PO₄ + _ HCl → 3NaCl + H₃PO₄
In reactant side we have 3 Na and we have the same amount in product side.
We also have 1 P and 4 O in both sides of the equation.
As we have 3 moles of NaCl in product side, this means we have:
NaCl → Na⁺ + Cl⁻
3 moles of Na⁺ and 3 moles of Cl⁻. In conclussion we need 3 moles of Cl⁻ in reactant side.Then, the stoichiometry of HCl must be, 3.
3 moles of HCl means that we have 3 moles of protons (H⁺).
HCl → H⁺ + Cl⁻
If you see the phosphoric acid, we also have 3 moles of protons.
H₃PO₄ → 3H⁺ + PO₄³⁻
Complete balanced equation is:
Na₃PO₄ + 3HCl → 3NaCl + H₃PO₄
