Aqueous sodium hydroxide is added to orange Na2Cr2O7 solution to give a yellow solution of X: Cr2O7^2- + 2OH^- -> 2CrO4^2- + H2O. X is then reduced by a stoichiometric amount of Fe^2+ in acidic medium to Cr^3+. The identity of X and the spin-only magnetic moment of the chromium species finally obtained (per ion) are:

JEE Advanced levelSingle correct optionDifficulty 3 of 3df146

Aqueous sodium hydroxide is added to orange $Na X_{2} Cr X_{2} O X_{7}$ solution to give a yellow solution of X: $Cr X_{2} O X_{7} X^{2 -} + 2 OH X^{-} 2 CrO X_{4} X^{2 -} + H X_{2} O$ . X is then reduced by a stoichiometric amount of $Fe X^{2 +}$ in acidic medium to $Cr X^{3 +}$ . The identity of X and the spin-only magnetic moment of the chromium species finally obtained (per ion) are:

The first equation is balanced, and X is chromate, Cr(VI)

d^{0}

. In acid,

CrO X_{4} X^{2 -} + 3 Fe X^{2 +} + 8 H X^{+} Cr X^{3 +} + 3 Fe X^{3 +} + 4 H X_{2} O

is balanced (charge +12 on both sides).

Cr X^{3 +}

3 d^{3}

n = 3

μ = 15 = 3.87 BM