Chemistry - Salt Analysis Question with Solution | TestHub

Iodine solution has a brown colour which disappears when iodine is reduced to iodide ion.

S₂O₃²⁻ (thiosulphate) reduces iodine to iodide and forms tetrathionate ion.

$${\mathrm{I}}_2+2{\mathrm{S}}_2{\mathrm{O}}_3^{2-}\to 2{\mathrm{I}}^{-}+{\mathrm{S}}_4{\mathrm{O}}_6^{2-}$$

Cl₂ also reacts with iodine by redox reaction, converting iodine into iodide/chlorine species.

Therefore, the colour of iodine disappears with S₂O₃²⁻ and Cl₂.

Answer: (A) S₂O₃²⁻ and (D) Cl₂