ADEQ Wastewater Collections 1 Practice Test 2026 - Free Wastewater Collection Practice Questions and Study Guide

Litmus paper is a simple pH indicator used to tell whether a solution is acidic or basic. Blue litmus paper changes color to red in acidic solutions, while red litmus paper remains red in acid and only turns blue in basic conditions. Since this question refers to litmus paper in an acidic solution, the blue paper would turn red. (Red litmus, if used, would stay red in acid.) Violet and yellow are not the standard color changes for litmus in acid–base testing. So red is the observed color.