Aqueous solution of a salt 'A', when mixed with NaOH solution and warmed, a black precipitate is formed. Black ppt. is filtered and dissolved in dil. H2SO4 solution. The resulting solution gives a cho

Question

Aqueous solution of a salt 'A', when mixed with NaOH solution and warmed, a 
black precipitate is formed. Black ppt. is filtered and dissolved in dil. H2SO4 
solution. The resulting solution gives a chocolate coloured precipitate with 
potassium ferrocyanide solution. The filtrate obtained after filtering off the 
black precipitate, upon warming with Zn and NaOH evolves a pungent smelling gas.
The resulting solution also responds to the ring test. The filtrate does not 
evolve any gas when it is boiled with urea in the presence of H2SO4.

Prashant Kotian · Accepted Answer

Correct answer: B. Step 1: The reaction of bismuth(III) ions with iodide ions (I-) initially forms a dark brown/black precipitate of bismuth(III) iodide (BiI3). Step 2: The black BiI3 precipitate reacts with excess iodide ions to form a highly stable, soluble tetraiodobismuthate(III) complex anion: BiI3 + I- -> [BiI4]-. Step 3: The [BiI4]- complex solution exhibits a characteristic orange/yellow-orange color. This confirms the presence of Bi3+, matching option (b).

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