You can't calculate the molarity of a solution with just the moles of solute and the volume of water. You need the total volume of the solution, not just the volume of the solvent (water).

Here's why:

* Molarity is defined as moles of solute per liter of solution.

* The solution is the combination of the solute (FeBr3) and the solvent (water).

To calculate the molarity, you need the following:

1. Moles of solute (FeBr3): You already have this (3 moles).

2. Total volume of the solution (in liters): This is missing from your information.

Example:

Let's say you dissolve those 3 moles of FeBr3 in enough water to make a total volume of 2 L. Then the molarity would be:

Molarity = (3 moles FeBr3) / (2 L solution) = 1.5 M

Important Note: It's generally not accurate to assume the volume of the solution is the same as the volume of the water added. When you dissolve a solute, the volume can change slightly.