Wustite has the composition Fe_0.93O with some Fe^2+ replaced by Fe^3+ so that the crystal is neutral. The percentage of the iron present as Fe^3+ is

JEE Advanced levelSingle correct optionDifficulty 3 of 3ss055

Wustite has the composition $Fe X_{0.93} O$ with some $Fe X^{2 +}$ replaced by $Fe X^{3 +}$ so that the crystal is neutral. The percentage of the iron present as $Fe X^{3 +}$ is

Let

y

be the number of

Fe X^{3 +}

per

O X^{2 -}

; then

2 (0.93 - y) + 3 y = 2

, so

y = 0.14

. Fraction of iron as

Fe X^{3 +} = 0.14/0.93 = 0.1505

, i.e. 15.1%. The value 14.0% is

y

itself, taken per oxygen.