A substance used to show visually the presence of acids or bases in a solution.

• A. Chemical Indicator
• B. Disaccharide
• C. Compound
• D. Carbohydrate

Answer: (A)

Acid-base indicators are substances that change color in response to the hydrogen ion concentration in a solution, letting you see visually whether a solution is acidic or basic. A chemical indicator is exactly that kind of substance—it alters its color as the pH changes, so you can tell if acids or bases are present by simply looking at the color change. For example, litmus turns red in acidic solutions and blue in basic ones; phenolphthalein is colorless in acidic conditions but pink in basic ones; methyl orange shifts from red in acidic solutions to yellow in basic ones. In contrast, a disaccharide and carbohydrates are types of sugars and do not indicate acidity or basicity; a compound is a general term for any chemical substance and doesn’t specify the visual indication of pH.