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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ev164

Select the correct statements about the dichromate reaction in COD determination, $Cr X_{2} O X_{7} X^{2 -} + 14 H X^{+} + 6 e X^{-} 2 Cr X^{3 +} + 7 H X_{2} O$ .

A1 mol of dichromate corresponds to 1.5 mol of $O X_{2}$
B1 mol of dichromate accepts 3 mol of electrons
COxidation of 1 mol of glucose needs 12 mol of $O X_{2}$
D1 mol of dichromate accepts 6 mol of electrons

Answer: A, D

The half reaction shows 6 electrons per dichromate. Since 1 mol of

O X_{2}

accepts 4 electrons,

6/4 = 1.5

mol of

O X_{2}

is equivalent. Glucose needs 6 mol of

O X_{2}

, not 12.

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