Question

Which of the following anion(s) is/are interfering radicals?
(A) $B{{O}_{3}}^{3-}$
(B) ${{F}^{-}}$
(C) $P{{O}_{4}}^{3-}$
(D) none of these

Answer 1

Third group reagents are ammonium chloride and ammonium hydroxide. Interfering radicals usually form during precipitation of third group. Hydrochloric acid and Ferric chloride is used mostly for the removal of different interfering radicals.

Complete step by step solution: Interfering radicals are anionic radicals like oxalate, tartrate, fluoride, borate and phosphate. They form complex compounds with third group reagents like ammonium chloride and ammonium hydroxide. They are usually used to form a complex with 3rd group which later leads to incomplete precipitation of 3rd group and results in immature precipitation of 5th group.
Group III cations, are $C{{r}^{3+}}$, $A{{l}^{3+}}$, $F{{e}^{3+}}$ and $N{{i}^{2+}}$ . All the Group III cations form insoluble sulfides or hydroxides in a basic solution saturated with ${{H}_{2}}S$. Ammonium chloride is added to ensure low concentration of hydroxide ions. The formation of a reddish-brown precipitate indicates $F{{e}^{3+}}$; a gelatinous white precipitate indicates $A{{l}^{3+}}$; and a green precipitate indicates $C{{r}^{3+}}$.
Test for phosphate -: test 0.5ml of the filtrate with 1ml ammonium molybdate reagent and a few drops of concentrated nitric acid, and warm gently, yellow precipitate indicates the presence of phosphate. Its composition is not known exactly.

Therefore, the interfering radicals are fluoride and phosphates (B) and (C) are the correct options.

Note: The "Group reagent" is a cocktail of reagents that serves as a prima facie indication of a particular cation, characterized by the formation of a precipitate during a positive test/result and no precipitation in the event of a negative test/result. Most common ammonium salts.