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COMEDK2025Chemistryd and f Block ElementsActual

Find the correct matches. array |l|l|l|l| A & Cr ₂ O ₇²⁻ & P & is predominantly a basic compound. B & FeCr ₂ O ₄ & Q & is predominantly an acidic compound. C & CrO ₃ & R & forms yellow chromate on reaction with Na ₂ CO ₃ in air. D & CrO & S & is interconvertible with MO ₄²⁻ depending on the pH of the medium. array

Options

  1. AA = R B = S C = P D = Q
  2. BA = R B = Q C = S D = P
  3. CA = S B = R C = Q D = P
  4. DA = S B = R C = P D = Q

Correct answer

C. A = S B = R C = Q D = P

Step-by-step solution

The dichromate ion Cr ₂ O ₇²⁻ exists in equilibrium with the chromate ion CrO ₄²⁻ depending on the pH of the medium, where Cr ₂ O ₇²⁻ + H ₂ O 2 CrO ₄²⁻ + 2 H ⁺ . Thus, A matches S. Chromite ore FeCr ₂ O ₄ reacts with Na ₂ CO ₃ in the presence of air to form sodium chromate, which is yellow. The reaction is 4 FeCr ₂ O ₄ + 8 Na ₂ CO ₃ + 7 O ₂ 8 Na ₂ CrO ₄ + 2 Fe ₂ O ₃ + 8 CO ₂ . Thus, B matches R. Chromium trioxide CrO ₃ is an acidic oxide because it dissolves in water to form chromic acid H ₂ CrO ₄ . Thus, C matches

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