A sodium salt X gives violet vapours with conc. H2SO4 and a bright yellow precipitate with AgNO3 insoluble in conc. ammonia. Chlorine water with CCl4 turns the organic layer violet, and then colourless with excess. X, the final oxidation state of iodine and the electrons lost per iodide ion converted to the final species are respectively

JEE Advanced levelSingle correct optionDifficulty 3 of 3qa054

A sodium salt X gives violet vapours with conc. $H X_{2} SO X_{4}$ and a bright yellow precipitate with $AgNO X_{3}$ insoluble in conc. ammonia. Chlorine water with $CCl X_{4}$ turns the organic layer violet, and then colourless with excess. X, the final oxidation state of iodine and the electrons lost per iodide ion converted to the final species are respectively

Violet vapours and a yellow precipitate insoluble in ammonia identify iodide. Excess chlorine oxidises I to iodate:

I X_{2} + 5 Cl X_{2} + 6 H X_{2} O 2 HIO X_{3} + 10 HCl

, so I is +5. The change from -1 to +5 is 6 electrons per ion. Starting from

I X_{2}

(0) gives 5, which is the trap. Bromide does not give violet

CCl X_{4}