Sodium carbonate extract is acidified with dilute HNO3, boiled, and treated with AgNO3. A pale yellow curdy precipitate P forms. P is only sparingly soluble in concentrated aqueous NH3 but dissolves completely in excess aqueous Na2S2O3. The anion in the extract and the formula of the complex formed with thiosulphate (thiosulphate acting as a monodentate ligand) are respectively

JEE Advanced levelSingle correct optionDifficulty 3 of 3qa107

Sodium carbonate extract is acidified with dilute $HNO X_{3}$ , boiled, and treated with $AgNO X_{3}$ . A pale yellow curdy precipitate P forms. P is only sparingly soluble in concentrated aqueous $NH X_{3}$ but dissolves completely in excess aqueous $Na X_{2} S X_{2} O X_{3}$ . The anion in the extract and the formula of the complex formed with thiosulphate (thiosulphate acting as a monodentate ligand) are respectively

A pale yellow precipitate sparingly soluble in concentrated ammonia is

AgBr

(AgCl dissolves easily, AgI not at all). With thiosulphate,

AgBr + 2 S X_{2} O X_{3} X^{2 -} [Ag (S X_{2} O X_{3}) X_{2}] X^{3 -} + Br X^{-}

. The charge is

+ 1 + 2 (- 2) = - 3

. Hence bromide and

[Ag (S X_{2} O X_{3}) X_{2}] X^{3 -}