The answer correct answer is 12.
The coefficient of H3PO4 is 12. The balanced chemical equation for the reaction is; 3P₄S₃ + 38NO₃⁻ + 20H⁺ + 8H₂O → 12H₃PO₄ + 9SO₄²⁻ + 38NO; The reaction is a redox reaction; where some elements undergo oxidation (loss of electrons) while the other undergo reduction (gaining of electrons). The half reaction for the reduction is; NO3- + 4H+ + 3e---> NO + 2H2O, while the oxidation half reaction is; P4S3 + 28 H2O --> H3PO4 + 3SO42- + 4H+ + 38 e-; To obtain a complete and balanced equation; we then multiply by the coefficients such that the electrons on both sides cancel and add the half reactions together. which eventually gives us; 3P₄S₃ + 38NO₃⁻ + 20H⁺ + 8H₂O → 12H₃PO₄ + 9SO₄²⁻ + 38NO
