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JEE Main levelOne or more correct optionsDifficulty 2 of 3eq143

In iodometry with excess KI in acidic medium, the liberated $I X_{2}$ is titrated with thiosulfate. Which statements about moles of thiosulfate equivalent to 1 mol of the oxidant are correct?

A $Cr X_{2} O X_{7} X^{2 -}$ (to $Cr X^{3 +}$ ): 6 mol thiosulfate
B $IO X_{3} X^{-}$ (to $I X_{2}$ with $I X^{-}$ ): 6 mol thiosulfate
C $MnO X_{4} X^{-}$ (to $Mn X^{2 +}$ ): 10 mol thiosulfate
D $Cu X^{2 +}$ (to $CuI$ ): 1 mol thiosulfate

Answer: A, B, D

Thiosulfate moles equal the electrons gained per mole of oxidant (n-factor).

Cr X_{2} O X_{7} X^{2 -}

gains 6 e

^{-}

(true),

IO X_{3} X^{-}

ends up as

I X_{2}

giving 3

I X_{2}

, i.e. 6 thiosulfate (true),

MnO X_{4} X^{-}

gains 5 e

^{-}

so 5 thiosulfate, not 10 (false),

Cu X^{2 +}

gains 1 e

^{-}

(true).

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