Here's how to determine the pH of a solution with a hydronium ion concentration of 0.001 M (which is the same as 1 x 10^-3 M):

Understanding pH

* pH is a measure of the acidity or alkalinity of a solution.

* It's calculated using the following formula:

pH = -log[H₃O⁺]

where [H₃O⁺] is the concentration of hydronium ions in moles per liter (M).

Calculation

1. Substitute the concentration:

pH = -log(1 x 10^-3)

2. Use the properties of logarithms:

pH = 3

Result

The pH of a solution with a hydronium ion concentration of 0.001 M is 3. This indicates that the solution is acidic.