On treating a solid salt A with dil. H_2SO_4 | vedclass

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(D) The reddish-brown fumes evolved on treating salt $A$ with dil. $H_2SO_4$ and warming indicate the presence of nitrite $(NO_2^-)$ ions,which produc

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$I^-$

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(D) The reddish-brown fumes evolved on treating salt $A$ with dil. $H_2SO_4$ and warming indicate the presence of nitrite $(NO_2^-)$ ions,which produce $NO_2$ gas. The reaction is: $2NO_2^- + 2H^+ \rightarrow H_2O + NO + NO_2$ (reddish-brown). The blue colour produced upon adding $C$,starch,and acetic acid is the characteristic test for iodine $(I_2)$. This implies that $C$ is an oxidizing agent that oxidizes $I^-$ (if present in $A$) or provides $I_2$ to react with starch. However,the question asks what $C$ may contain to produce the blue colour with the salt solution of $A$. Since $A$ contains $NO_2^-$,and the test for $I^-$ involves oxidation to $I_2$ (which turns starch blue),$C$ must be an oxidizing agent like $NO_2^-$ itself or a reagent that facilitates the reaction. Given the options,$I^-$ is the species that reacts to form $I_2$,but the question asks what $C$ contains to produce the blue colour. Actually,the reaction of $NO_2^-$ with $I^-$ in acidic medium produces $I_2$. Thus,$C$ must contain $I^-$.

List-$I$ ($Test$/$reagent$)	List-$II$ ($Radical$ $identified$)
$A$. Lake Test	$I$. $NO_3^{-}$
$B$. Nessler's Reagent	$II$. $Fe^{3+}$
$C$. Potassium thiocyanate	$III$. $Al^{3+}$
$D$. Brown Ring Test	$IV$. $NH_4^{+}$

On treating a solid salt $A$ with dil. $H_2SO_4$ and warming,reddish-brown fumes of gas $B$ are evolved. Addition of $C$ to the salt solution of $A$ followed by freshly prepared starch solution and acidification with acetic acid produces a blue colour. $C$ may contain:

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