A solution is 12.5% Na3PO, by mass. How many grams of Na3PO4 are there in a 35.9mL solution of Na3PO, if the density of the
solution is 1.10g/mL?

Explanation:

Mass of solution of Na₃PO₄ = volume  × density

                                              =   35.9 mL × 1.10 g/mL

                                              =   39.49 g

Now, since the solution only contains 12.5% Na₃PO₄, then the mass of Na₃PO₄ is 12.5% of 39.49 g

                                 12.5% × 39.49 g = 4.94 g          

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particle   p is an electron and particle q is a neutron