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Question:

Given below are the half-cell reactions: Mn²⁺ + 2e⁻ → Mn; E⁰ = -0.18 V
2(Mn³⁺ + e⁻ → Mn²⁺); E⁰ = +1.51 V. The E⁰ for 3Mn²⁺ → Mn + 2Mn³⁺ will be:

-0.33V;the reaction will not occur

-2.69V;the reaction will occur

-0.33V;the reaction will occur

-2.69V;the reaction will not occur

Solution:

Adding equation 2 from 1 gives 3Mn²⁺ → Mn + 2Mn³⁺
Hence, E⁰ for this reaction = (-0.18) - (+1.51) V = -1.69 V.
The reaction will not occur as E⁰cell is negative value as for spontaneous reaction value should be positive. Option D is correct.