Final answer:
The pH of a 4.5 × 10⁻³ M solution of HNO₃ is calculated to be 2.35, which indicates that the solution is acidic since its [H₃O⁺] is greater than 1 × 10⁻⁷ M. Therefore, the correct answer is A) acidic.
Step-by-step explanation:
The pH of a 4.5 × 10⁻³ M solution of HNO₃ can be determined by taking the negative logarithm of the hydrogen ion concentration. The formula to find pH is pH = -log[H⁰⁺]. Since HNO₃ is a strong acid, it fully dissociates in water, thus [H⁰⁺] = 4.5 × 10⁻³ M.
Using the formula: pH = -log(4.5 × 10⁻³), we calculate the pH.
pH = -(-2.35) = 2.35
Considering that a solution is acidic if [H₃O⁺] > 1 × 10⁻⁷ M, the given solution of HNO₃ with [H₃O⁺] = 4.5 × 10⁻³ M is indeed acidic. So the correct option is A) acidic.