See image below for the lewis structure of acrolein
7 becuse it splits in half
Na3PO4*12H2O + BaCl2*2H2O = Ba3(PO4)2 + NaCl + H2O
add barium chloride to your Na3PO4.12H2O a white precipitate of Ba3(PO4)2 will be formed wrt salt(NaCl) and water(H20) if Na3PO4.12H2O. will be there.
7.8 g/cm3 because Mass/Volume=Density