To find the molarity of NH3, we first need to calculate the number of moles of NH3 present.

The balanced equation for the reaction is:
NH3 -> N + 3H

From the balanced equation, we can see that 1 mole of NH3 produces 1 mole of N and 3 moles of H.

Given that there are 2.5 moles of NH3 present, we can calculate the moles of N and H produced:
Moles of N = 2.5 moles
Moles of H = 2.5 moles * 3 = 7.5 moles

Now, we can calculate the total moles of NH3 and the total volume in liters to find the molarity:

Total moles of NH3 = 2.5 moles
Total volume in liters = ?

Given in the problem is that the volume is not given, so we cannot calculate the molarity without knowing the volume of the solution.