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JEE Main levelSingle correct optionDifficulty 2 of 3qa027

In the reaction $2 NO X_{2} X^{-} + 2 I X^{-} + 4 H X^{+} 2 NO + I X_{2} + 2 H X_{2} O$ used in the starch-iodide test for nitrite, the oxidising agent and the change in oxidation state of nitrogen are respectively

A $H X^{+}$ ; +3 to +5
B $I X^{-}$ ; +3 to +2
C $NO X_{2} X^{-}$ ; +3 to +4
D $NO X_{2} X^{-}$ ; +3 to +2

Answer: D

Nitrogen goes from +3 in

NO X_{2} X^{-}

to +2 in NO, so it is reduced and nitrite is the oxidising agent. Iodide is oxidised to

I X_{2}

, which gives a blue-black colour with starch. The N oxidation state does not rise to +4 or +5.

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