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A small amount of sodium peroxide (Na2O2) is added to an acidified dichromate solution and the mixture is shaken. The observation is:

1. Appearance of blue colour
2. Orange colour turning to green
3. Vigorous liberation of oxygen gas
4. Formation of a bluish-green precipitate

Correct answer: Appearance of blue colour

Solution

Na2O2 furnishes H2O2 which reacts with acidified dichromate to form the deep-blue chromium peroxide CrO5, giving a blue colour.

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