It is a white-coloured substance that is insoluble in water.

The appearance of the solution is determined by the physical properties of the product formed in the reaction.

• It is a white-coloured substance that is insoluble in water. This is correct. Calcium carbonate is a white solid. Because it does not dissolve in water (it is insoluble), it forms tiny particles that remain suspended, scattering light and making the solution look milky or cloudy.
• It is a colourless gas. This is incorrect. Carbon dioxide is a colourless gas, but it is a reactant, not the product causing the milkiness.
• It is a clear liquid that is soluble in water. This is incorrect. If the product were soluble, the solution would remain clear.
• It is a black-coloured solid. This is incorrect. Calcium carbonate is white.

Ok