A substance that turns blue litmus red is:
- A. A base
- B. An acid
- C. A salt only
- D. Distilled water
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Correct option: B — An acid
Acids turn blue litmus red; bases turn red litmus blue.
Class 10 Science Chapter 2
All questions
4 Practice Questions — The answers are hidden. Reveal them to check your answers. The Timed Test will be available in Phase 3.
The pH of a neutral solution at 25 °C is:
- A. 0
- B. 7
- C. 14
- D. 1
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Correct option: B — 7
pH 7 is neutral at 25 °C; below 7 acidic, above 7 basic.
Why is the pH of the mouth important for tooth decay?
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If mouth pH falls below about 5.5, enamel (calcium phosphate) starts dissolving. Bacteria produce acid from sugar, so rinsing and cleaning keeps pH safer.
Link sugar → acid → low pH → enamel damage.
Differentiate acids and bases on the basis of ions, litmus and a daily-life example each.
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Acids produce H⁺ (or H₃O⁺) in water, taste sour, turn blue litmus red — e.g. lemon juice / HCl.
Bases produce OH⁻, feel soapy, turn red litmus blue — e.g. soap solution / NaOH.
They neutralise each other to give salt and water.
Mention one strong and one weak example if the question has marks for that.
Next step
These practice sets use original GKSchools wording — they are not a verbatim dump of the NCERT textbook. “Important” means high-weight practice for the chapter, not a claim that these are previous-year exam questions.
