Here's how to determine the pH of a solution with a hydronium ion concentration of 10^-4:

Understanding pH

* pH is a measure of the acidity or alkalinity of a solution. It's based on the concentration of hydronium ions (H₃O⁺).

* The formula for pH is: pH = -log[H₃O⁺]

Calculation

1. Substitute the hydronium ion concentration into the formula:

pH = -log(10^-4)

2. Use the rule of logarithms: log(a^b) = b*log(a)

pH = -(-4 * log(10))

3. Simplify: log(10) = 1

pH = 4

Answer: The pH of a solution with a hydronium ion concentration of 10^-4 is 4.