What is the result of testing ammonia with damp red litmus paper?

• A. Paper turns blue
• B. Paper turns red
• C. Paper remains unchanged
• D. Paper turns purple

Answer: (A)

Testing with red litmus paper shows whether a substance is acidic or basic. Ammonia is a base, so when it contacts damp red litmus paper, it turns blue. The dampness lets ammonia dissolve a little and react with water to form hydroxide ions, raising the pH and causing the red paper to shift to blue. This contrast (red turning blue) signals basicity. An acid would keep the paper red, neutral wouldn’t change it, and purple isn’t a standard result for this test, so blue is the correct outcome.