How can you determine the pH of a solution using litmus paper?

Litmus paper is a useful indicator for determining the pH of a solution by observing color changes. When you immerse litmus paper into a solution, the paper changes color depending on the acidity or alkalinity of the solution.

In the case of acidic solutions, litmus paper typically turns red, while in basic solutions, it changes to blue. By comparing the color of the paper to a standardized color scale that correlates specific colors to pH levels, one can identify whether a solution is acidic, neutral, or basic and determine its approximate pH value. This method is quick and provides visual confirmation of the solution's acidity or alkalinity.

The other methods listed do not provide a direct measurement of pH. Measuring the volume of the solution does not indicate its acidity or basicity, observing temperature changes may not correlate with pH, and simply adding a strong acid would alter the solution's pH rather than determine it. Thus, using litmus paper and comparing it to a color scale is the correct and effective approach to assessing the pH of a solution.