Final answer:
In the presence of an acid, litmus paper appears red due to acids turning blue litmus paper to red, while in the presence of a base, litmus paper appears blue, as bases turn red litmus paper blue.
Step-by-step explanation:
In the presence of an acid, litmus paper appears red.
This is because acids turn blue litmus paper to red but do not change the color of red litmus paper. In the presence of a base, litmus paper appears blue.
Bases, such as soap and cleaning agents, turn red litmus paper blue, demonstrating their alkaline properties.
It is important to recognize that litmus paper is a simplistic form of pH paper that provides a visual representation of acidity or alkalinity of a substance.
Different indicators like phenolphthalein are used to provide more detailed information about the pH level, such as turning pink in a basic solution, while remaining colorless in an acid.