1. Calculate the molarity of the nitric acid solution:

* Molar mass of HNO₃: 1 (H) + 14 (N) + 3 * 16 (O) = 63 g/mol

* Moles of HNO₃: 12.6 g / 63 g/mol = 0.2 mol

* Molarity (M): 0.2 mol / 0.250 L = 0.8 M

2. Nitric acid is a strong acid, so it completely ionizes in solution:

HNO₃ (aq) → H⁺ (aq) + NO₃⁻ (aq)

This means that the concentration of H⁺ ions is equal to the concentration of the nitric acid solution.

3. Calculate the pH:

* pH = -log[H⁺]

* pH = -log(0.8)

* pH ≈ 0.1

Therefore, the pH of the 250.0 ml aqueous solution containing 12.6 g of nitric acid is approximately 0.1.