What is the molarity of a solution that contains 3.25 moles of nano3 in 250. ml of solution?

The formula for this solution to find the molarity is: molarity = moles/liters

First, you would have to convert the milliliters to liters.
So, 250 ml = 0.25 L 
Now that it has been converted, we can continue with solving the molarity as follows:
m = mol/L
m = 3.25/0.25 
m = 13

The molarity of the solution given is 13

Let me know if you need further info. :)

               - Dotz