The balanced reaction is
(Na3PO4)12H2O + 9(BaCl2)2H2O → 6Ba3(PO4)2 + 36NaCl + 10H2O
molar mass of (Na3PO4)12H2O = 380 g/mol
given mass of (Na3PO4)12H2O = 0.990 g
moles of (Na3PO4)12H2O = given mass/molar mass
moles of (Na3PO4)12H2O = 0.990/380= 0.0026 mole
one mole of (Na3PO4)12H2O forms 6 mole of Ba3(PO4)2
0.0026 mole of (Na3PO4)12H2O forms 0.0026×6 =
0.0156 mole of Ba3(PO4)2
mass of 0.0156 moles of Ba3(PO4)2 is = 0.0156 × 601.9 g = 9.40 gram