CBSE Class 10 Sample Paper Science Solution - For 2023 Boards

Class 10
Solutions to CBSE Sample Paper - Science Class 10

The change in colour of the moist litmus paper in the given set up is due to

Question 1- The change in colour - teachoo.jpg

  1. presence of acid
  2. presence of base
  3. presence of H⁺(aq) in the solution
  4. presence of Litmus which acts as an indicator
  1. i and ii
  2. Only ii
  3. Only iii
  4. Only iv



  • Litmus is an indicator that indicates the presence of acids or bases by changing its colour.
  • When an acid is added to litmus, it changes its colour to red .
  • When a base is added it changes its colour to blue
  • In the figure, conc H 2 SO 4 is being added to a tube containing NaCl

The following reaction takes place:

Reaction between H2SO4 and NaCl - Teachoo.jpg

  • Here, HCl is liberated in the form of a gas .
  • Since HCl is an acid, the litmus turns red due to the HCl gas.
  • The acid causes the solution to have H+ ions .

Therefore, the correct answer is (c) only (iii)

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo