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Which of the following statements is INCORRECT? (I) Bleaching powder is a pale yellow powder. (II) Dry NH3 gas turns red litmus blue. (III) The pH of rainwater is nearly 7. (IV) The pH of acid rain is nearly 5.6.

Which of the following statements is INCORRECT? (I) Bleaching powder is a pale yellow powder. (II) Dry NH3 gas turns red litmus blue. (III) The pH of rainwater is nearly 7. (IV) The pH of acid rain is nearly 5.6. Correct Answer Only II)

  • Litmus is an acid-base indicator for aqueous solution
  • The un-ionized litmus is red, whereas the ion is blue in colour. When there is sufficient OH- ions in the medium,  the weak acid is converted to its salt, so blue colour predominates.
  •  In acidic solutions, however, the non-ionic form predominates, hence the red colour. 
  • Ammonia is basic in nature.
  • Dry ammonia produces no hydroxide OH- ions. So there is no action on litmus paper.
  • Besides a solution of ammonia in water releases OH- ions. Therefore, the litmus paper turns Red litmus to blue. 

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