(a) Write the formula of the ions which (i) acids, and (ii) bases generate in water solutions. (b) Dry HCl gas does not change the colour of dry litmus paper. Why? (a) Write the formula of the ions which (i) acids, and (ii) bases generate in water solutions. (b) Dry HCl gas does not change the colour of dry litmus paper. Why?

ScienceCBSE Class 10 · Board exam 2025, set 31/3/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 22

Set in the CBSE Class 10 board exam of 2025, paper 31/3/1, section B, question 22, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 2 marks · Very short answerAcids, Bases and Salts

(a) Write the formula of the ions which (i) acids, and (ii) bases generate in water solutions.

(b) Dry HCl gas does not change the colour of dry litmus paper. Why?

(a)
Write the formula of the ions which (i) acids, and (ii) bases generate in water solutions.
0 marks
(b)
Dry HCl gas does not change the colour of dry litmus paper. Why?
0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/3/1.

Hints

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

Hint 1

Acidic properties come from a particular ion formed only in water.

Hint 2

What is missing when both the gas and the litmus are dry?

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.

(a)(i) Acids give hydrogen ions, $H^{+}$ , which exist as hydronium ions $H_{3} O^{+}$ in water.
½ mark
(a)(ii) Bases give hydroxide ions, $O H^{-}$ , in water.
½ mark
(b) Dry HCl gas does not dissociate into $H^{+}$ ions without water, so no acidic behaviour is shown and dry litmus does not change colour.
1 mark

Answer: (a)(i) $H^{+}$ / $H_{3} O^{+}$ ; (ii) $O H^{-}$ ; (b) no $H^{+}$ ions are formed without water

Where the marks are

$H^{+}$ or $H_{3} O^{+}$ for acids (½ mark)
$O H^{-}$ for bases (½ mark)
Dry HCl does not ionise to give $H^{+}$ ions without water (1 mark)

Revise the chapter

Chapter: Acids, Bases and Salts (notes, formulas, where marks are lost and every past question)
Topic: Chemical Properties of Acids and Bases

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 paper2025 board paper, set 31/3/1: every question, by section.

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CBSE Class 10 Science 2025: question 22

Hints

Step-by-step solution

Revise the chapter

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