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Question:

The standard reduction potentials for Zn2+|Zn, Ni2+|Ni and Fe2+|Fe are -0.76, -0.23 and -0.44 V respectively. The reaction X + Y2+ → X2+ + Y will be spontaneous when:

X=Ni, Y=Fe

X=Zn, Y=Ni

X=Ni, Y=Zn

X=Fe, Y=Zn

Solution:

For the reaction to be spontaneous, its Eocell should be positive
A) Eocell = -0.44 + 0.23 = -0.21
B) Eocell = -0.76 + 0.23 = -0.53
C) Eocell = -0.76 + 0.44 = -0.32
D) Eocell = -0.23 + 0.76 = +0.53
Hence, option D is the correct answer.