You're asking for a bit of a trick question! The molarity of a solution *doesn't* change based on its density. Molarity is defined as moles of solute per liter of solution.

Here's why:

* Molarity (M): Represents the concentration of a solution. It tells you how many moles of a substance (solute) are dissolved in a specific volume (usually liters) of the solution.

* Density: Is a measure of mass per unit volume. In this case, it tells you how much mass of the solution is packed into each milliliter.

The given density information (1.015 g/mL) doesn't affect the molarity of the solution. The solution is already stated to be 0.142 M Na₃PO₄.

Explanation:

Imagine you have a 1-liter solution of 0.142 M Na₃PO₄. This solution contains 0.142 moles of Na₃PO₄. Whether the solution is dense or less dense, the amount of Na₃PO₄ present in that liter remains the same, so the molarity stays constant.

Important Note: If you wanted to calculate the *mass* of Na₃PO₄ present in a certain volume of the solution, then the density would be important.