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In the iodometric titration of liberated iodine with sodium thiosulphate, starch indicator is added:

  1. Aat the very beginning, before any thiosulphate is added
  2. Bimmediately after the end point is passed
  3. Cwhen the solution has faded to a pale yellow, close to the end point
  4. Dafter the blue colour has first appeared at the end point

Answer: C

Starch forms a dark blue complex with a large amount of iodine that dissociates slowly, which makes the end point sluggish. So it is added near the end point, when the iodine colour has become pale yellow, and the sharp disappearance of the blue colour marks the end.
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