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JEE MainChemistryd and f Block Elements

A pungent-smelling gas, obtained by treating a sulfite salt with dilute H ₂ SO ₄ , is passed into an acidified orange solution of potassium dichromate. The solution turns green. The chemical formula of the chromium-containing compound responsible for this green colour is:

Options

  1. ACrSO ₄
  2. BCr ₂( SO ₄)₃
  3. CCr ₂ O ₃
  4. DK ₂ CrO ₄

Correct answer

B. Cr ₂( SO ₄)₃

Step-by-step solution

The pungent-smelling gas evolved on treating a sulfite salt with dilute H ₂ SO ₄ is sulfur dioxide ( SO ₂ ). When SO ₂ is passed through an acidified solution of potassium dichromate ( K ₂ Cr ₂ O ₇ ), it acts as a reducing agent. It reduces the chromium from the +6 oxidation state to the +3 oxidation state. The balanced chemical equation is: K ₂ Cr ₂ O ₇ + H ₂ SO ₄ + 3 SO ₂ K ₂ SO ₄ + Cr ₂( SO ₄)₃ + H ₂ O The green colour of the resulting solution is due to the formation of aqueous chromium(III) sulfate, Cr ₂( SO ₄

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