A salt solution containing chloroform is treated with chlorine water and the chloroform layer turns purple. What anion is present in the salt?

Chlorine ($\text{Cl}_2$) is a stronger oxidizing agent than bromine ($\text{Br}_2$) and iodine ($\text{I}_2$). Therefore, chlorine water can oxidize bromide ions ($\text{Br}^{-}$) to bromine and iodide ions ($\text{I}^{-}$) to iodine.

• Reaction with bromide: $\text{Cl}_2(\text{aq}) + 2\text{Br}^{-}(\text{aq}) \to 2\text{Cl}^{-}(\text{aq}) + \text{Br}_2(\text{aq})$
• Reaction with iodide: $\text{Cl}_2(\text{aq}) + 2\text{I}^{-}(\text{aq}) \to 2\text{Cl}^{-}(\text{aq}) + \text{I}_2(\text{aq})$

Chloroform ($\text{CHCl}_3$) is an organic solvent that is immiscible with water. It is used to extract the non-polar halogens ($\text{Br}_2$ and $\text{I}_2$) from the aqueous solution, making their characteristic colors more visible.

• When bromine ($\text{Br}_2$) is extracted into chloroform, it typically produces an orange-brown or yellow-brown color.
• When iodine ($\text{I}_2$) is extracted into chloroform (or other non-polar organic solvents like carbon tetrachloride or hexane), it produces a distinct purple or violet color.

The question states that the chloroform layer turns purple. This color is characteristic of iodine ($\text{I}_2$) dissolved in chloroform. Since iodine is produced by the oxidation of iodide ions ($\text{I}^{-}$) by chlorine water, the salt must contain iodide ions.

The final answer is $\text{D}$