Redox reactions play a pivotyal role in chemistry and biology. The values of standard redox potential `(E^(@))` of two half-cell reactions decide which way the reaciton is expected to proced. A simple exampler is a Daniel cell in which zinc goes into solution and copper gerts deposited. Given below are a set of half-cell reactions (acidic medium) along with their `E^(@)` (`V` with respect to normal hydrofgen electrode) values. Using this data :
`I_(2) + 2e^(-) rarr 2I^(-)" " E^(@) = 0.54`,
`CI_(2) + 2e^(-) rarr 2CI^(-) " "E^(@) = 1.36`,
. `Mn^(3+) + e^(-) rarr Mn^(2+) " "E^(@) = 1.50`,
`Fe^(3+) + e^(-) rarr Fe^(2+)" " E^(@) = 0.77`,
`O_(2) + 4H^(+) + 4e^(-) rarr 2H_(2)O " "E^(@) = 1.23`,
Soldium fusion extract, obtained from aniline, on treatment with iron `(II)` sulphatge and `H_(2)SO_(4)` in presence of air gives a Prussion bule precipitate. The blue colour is due to the formation of :

Options

A. `Fe_(4)[Fe(CN)_(6)]_(3)`
B. `Fe_(3)[Fe(CN)_(6)]_(2)`
C. `Fe_(4)[Fe(CN)_(6)]_(2)`
D. `Fe_(3)[Fe(CN)_(6)]_(3)`

Answer

A

Explanation

`Na + C + N rarr NaCN`
`Fe^(2+) + 6CN^(-) rarr [Fe(CN)_(6)]^(4-)`
`4Fe^(3+) + 3[Fe(CN)_(6)]^(4-) rarr underset("Prussion blue")(Fe_(4)[Fe(CN)_(6)]_(3darr)`