Assertion :When moist starch iodide paper comes in contact with chlorine, it turns blue back. Reason: Free iodine is liberated from potassium iodide.

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

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Assertion is correct but Reason is incorrect

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Both Assertion and Reason are incorrect

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Solution

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
This is a common test for chlorine. Starch-iodide paper is white in colour and made by dipping a filter paper in a solution of starch and potassium iodide. Chlorine is more reactive than iodine. Therefore, when chlorine comes in contact with starch-iodide paper, it displaces iodine from potassium iodide. The free iodine ions then react with starch present on the paper, turning it blue-black in colour.
$2 K I + C l_{2} \to 2 K C l + I_{2}$

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