In alkaline medium, 2[Cr(OH)4]- + 3H2O2 + 2OH- -> 2CrO4^2- + 8H2O. The number of moles of H2O2 required to oxidise one mole of Cr^3+ (as [Cr(OH)4]-) is

JEE Main levelSingle correct optionDifficulty 2 of 3qc192

In alkaline medium, $2 [Cr (OH) X_{4}] X^{-} + 3 H X_{2} O X_{2} + 2 OH X^{-} 2 CrO X_{4} X^{2 -} + 8 H X_{2} O$ . The number of moles of $H X_{2} O X_{2}$ required to oxidise one mole of $Cr X^{3 +}$ (as $[Cr (OH) X_{4}] X^{-}$ ) is

Cr goes from +3 to +6 (3 electrons).

H X_{2} O X_{2}

accepts 2 electrons, so

3/2 = 1.5

mol per mol Cr, matching 3

H X_{2} O X_{2}

for 2 Cr in the equation. The yellow chromate is later confirmed as yellow PbCrO4.