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JEE MainChemistryRedox Reactions

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Potassium permanganate ( KMnO ₄ ) is not used as a primary standard in redox titrations. Reason (R) : KMnO ₄ is highly hygroscopic and absorbs moisture from the atmosphere rapidly. In the light of the above statements, choose the most appropriate answer from the options given below :

Options

  1. ABoth (A) and (R) are correct and (R) is the correct explanation of (A)
  2. B(A) is correct but (R) is not correct
  3. CBoth (A) and (R) are correct but (R) is not the correct explanation of (A)
  4. D(A) is not correct but (R) is correct

Correct answer

B. (A) is correct but (R) is not correct

Step-by-step solution

Assertion (A) is correct because KMnO ₄ is a secondary standard. It is difficult to obtain in a perfectly pure state and usually contains traces of MnO ₂ . Reason (R) is incorrect because KMnO ₄ is not highly hygroscopic. The primary reasons it fails as a primary standard are its instability in aqueous solution (it slowly oxidizes water), its decomposition catalyzed by light, and its reactivity with trace organic matter. Reagents like NaOH are the ones rejected for being deliquescent and absorbing moisture. Answer:

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