A red solid is insoluble in water but soluble in the presence of KI. Heating the red solid in a test tube result in the formation of yellow sublimate in the part of the test tube. The red solid is:

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Prashant Kotian · Accepted Answer

Correct answer: B. Step 1: Cobalt(II) chloride hexahydrate (CoCl2.6H2O) exists as reddish-pink crystals. Step 2: Upon heating, it loses its water of crystallization to form anhydrous cobalt(II) chloride, which has a deep blue color: CoCl2.6H2O (pink) --Δ--> CoCl2 (blue) + 6H2O (vapour). Step 3: When water is added back to the blue anhydrous residue, it readily rehydrates to restore the pink hexahydrate, CoCl2.6H2O. This matches option (c).

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