Consider the following half cell reactions :
`Mn^(2+) + 2e^(-) to Mn E^(@) = -1.18 V`
`Mn^(2+) to Mn^(3+) + e^(-)E^(@0 = -1. 51 V`
The `E^@` for the reaction `3Mn^(2+) to Mn + 2Mn^(3+)`, and the possibility of the forwad reactions are respectively

Options

A. 2.69V and spontaneous
B. `-2.69` and non spotaneous
C. 0.33V and Spontaneous
D. 4.18 V and non spontaneous

Answer

B

Explanation

`Mn^(2+) + 2e^(-) to Mn (E_("Red")^(@)) = 1.18 V`
`2[Mn^(2+) + e^(-)] (E_("ox")^(@)) = -151 V`
`3Mn^(2+) to Mn^(3+) + 2 Mn^(3+) E_("cell")^(@) = ?`
`E_("cell")^(@) = (E_("ox")^@) + (E_("Red")^@)`
`= -1.51 - 1.18` and non spontaneous
`=2.69 V`
Since `E^@` is -ve `DeltaG` is +ve and the given forward cell reaction is non-spotaneous.