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The pH plays an important… (Class 10 Science 2026, Q28)

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ScienceCBSE Class 10 · Board exam 2026, set 31/4/1 · 4 marks · Case-based

CBSE Class 10 Science 2026: question 28

Set in the CBSE Class 10 board exam of 2026, paper 31/4/1, section B, question 28, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 4 marks · Case-basedCompetency-basedAcids, Bases and Salts

The pH plays an important role in our daily life. Strength of acids and bases depends on the number of ions and ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution.

Answer the following:

  1. (a)

    What type of indicator is used to predict how strong an acid or base is?

    0 marks
  2. (b)

    Three solutions A, B and C showed pH as 3, 5 and 7. Which solution has the highest concentration of ions?

    0 marks
  3. (c)

    What are strong acids and weak acids?

    0 marks

  4. OR

    (c)

    OR (i) Under what condition is rainwater called acid rain? (ii) In the following acids, identify weak acids: Nitric acid, hydrochloric acid, acetic acid, sulphuric acid, formic acid.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/4/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Litmus only tells acid or base. Which indicator shows a range of colours?

Hint 2

How do pH and H concentration change relative to each other?

Hint 3

Compare how completely the acids ionise in water.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (a) A universal indicator, a mixture of indicators that shows different colours at different pH values, is used to judge how strong an acid or base is.

    1 mark

  2. (b) Solution A (pH = 3) has the highest H ion concentration, because the lower the pH, the higher the H concentration.

    1 mark

  3. (c) Strong acids ionise almost completely in water and give a large number of H ions, e.g. HCl and HSO (pH about 1–2).

    1 mark

  4. Weak acids ionise only partly in water and give fewer H ions, e.g. acetic acid (pH closer to 7).

    1 mark

  5. (c) OR (i) Rainwater is called acid rain when its pH is less than 5.6.

    (ii) The weak acids in the list are acetic acid and formic acid.

Answer: (a) Universal indicator. (b) A (pH 3). (c) Strong acids give many H ions; weak acids give few H ions. OR: (i) pH < 5.6; (ii) acetic acid and formic acid.

Where the marks are

  • Names the universal indicator (1 mark)
  • Chooses solution A (1 mark)
  • Explains that strong acids give more H ions in water (1 mark)
  • Explains that weak acids give fewer H ions in water (1 mark)
  • OR: States pH < 5.6 for acid rain (1 mark); names acetic and formic acid as weak acids (½ + ½ marks)

Revise the chapter

Practise this chapterBoard-style questions from Acids, Bases and Salts, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/4/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.