Question

A colorless salt $A$ decolorizes the color of $I_3^{\ominus }$. Solution of $A$ on treatment with $AgN{O}_3$ gives white precipitate. The compound $A$ turns $FeC{l}_3$ solution (yellow) to $FeC{l}_2$ solution (green). Identify $A$.

• A. $N{a}_{2}S$
• B. $N{a}_2{S}_2{O}_3$
• C. $N{a}_{2}C{O}_3$
• D. $N{a}_{2}S{O}_4$

Answer 1

The correct option is B $N{a}_2{S}_2{O}_3$

Option (B) is correct.
$N{a}_2{S}_2{O}_3$ decolorizes the color of $I_3^{-}$. Solution of $N{a}_2{S}_2{O}_3$ on treatment with $AgN{O}_3$ gives white precipitate of $A{g}_2{S}_2{O}_3$.
$N{a}_2{S}_2{O}_3$ also turns $FeC{l}_3$ solution (yellow) to $FeC{l}_2$ solution (green).