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a) The cell reaction is :

2Cr + 3Fe²⁺→ 2Cr³⁺ + 3Fe

To calculate the emf of the cell, we apply the Nernst equation:

Where n = number of electrons involved in the cell reaction

∴ n = 6

E^°_cell = 0.261 V (given)

Fe²⁺ = 0.01M , Cr³⁺ = 0.01M (given)

By putting R = 8.314 JK^-1 mole^-1

T = 298K

F = 96500 coulombs

We get,

E_cell = 0.2807 V

Thus, the emf of the cell at 298 K is 0.2807 V

b) A is better for coating the surface of iron to prevent corrosion, because its E⁰ value (-2.3V) is more negative.