1. Calculate the moles of ammonium chloride (NH₄Cl)

* Molar mass of NH₄Cl: 53.49 g/mol

* Moles of NH₄Cl: (2.5 g) / (53.49 g/mol) = 0.0467 mol

2. Calculate the moles of ammonia (NH₃)

* Volume of ammonia solution: 125 cm³ = 0.125 dm³

* Moles of ammonia: (0.24 mol/dm³) * (0.125 dm³) = 0.03 mol

3. Calculate the concentrations of NH₄⁺ and NH₃

* Concentration of NH₄⁺: (0.0467 mol) / (0.125 dm³) = 0.374 mol/dm³

* Concentration of NH₃: (0.03 mol) / (0.125 dm³) = 0.24 mol/dm³

4. Use the Henderson-Hasselbalch equation

The Henderson-Hasselbalch equation relates pH, pKa, and the concentrations of the acid and conjugate base:

pH = pKa + log ([conjugate base] / [acid])

* pKa of ammonium ion (NH₄⁺): 9.25 (You can find this in a table of acid dissociation constants)

* [conjugate base] = [NH₃]

* [acid] = [NH₄⁺]

5. Substitute the values and calculate the pH

pH = 9.25 + log (0.24 mol/dm³ / 0.374 mol/dm³)

pH = 9.25 - 0.19

pH ≈ 9.06

Therefore, the pH of the buffer solution is approximately 9.06.