Q1
An acid turns blue litmus paper:
Ared
Bblue
Cgreen
Dcolourless
CBSEClass 7 (CBSE)ScienceCh 2 · Topic 1
Acids and Bases
Learning to identify substances as acidic or basic using their properties.
Core concept
Litmus is a natural dye extracted from lichens, commonly used as an acid-base indicator because of its clear colour change. Other natural indicators include turmeric (turns reddish-brown in bases) and red cabbage juice (turns pink in acids, green in bases). The strength of an acid or base can be more precisely measured using the pH scale, which ranges from 0 (strongly acidic) to 14 (strongly basic), with 7 being neutral (like pure water).
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CBSE class 7 acids and bases
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• Acids taste sour and turn blue litmus red; examples: lemon juice, vinegar, curd.
• Bases taste bitter, feel soapy, and turn red litmus blue; examples: soap, baking soda.
• Litmus, turmeric, and red cabbage juice are natural acid-base indicators.
• The pH scale (0-14) measures acid/base strength; 7 is neutral.