CBSE Class 7 Science
Question 1 of 19
Exploring Substances Acidic Basic and Neutral — Question 1
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Question What are these red and blue litmus paper strips made of? Why do they change colour when drops of some samples are put on them? (Page 10)
Red and blue litmus paper strips are made from paper soaked in an extract of lichens. They change colour when they come in contact with acidic or basic substances. Acidic substances turn blue litmus to red, and basic substances turn red litmus to blue.