Question

A reddish-pink substance on heating gives off a vapour which condenses on the sides of the test tube and the substance turns blue. If on cooling water is added to the residue it turns to original colour. The substance is ______.

Options

• Iodine crystals

• Copper sulphate crystals

• Cobalt chloride crystals

• ZnO

Answer 1

A reddish-pink substance on heating gives off a vapour which condenses on the sides of the test tube and the substance turns blue. If on cooling water is added to the residue it turns to original colour. The substance is Cobalt chloride crystals.

Explanation:

Cobalt chloride is a reddish-pink substance that, when heated, emits a vapour that condenses on the side of the test tube, turning it blue. When cool water is added to the residue, it returns to its original colour.