`E_(Mn)^(@)+7|""_(Mn)+2` = 1.5 V `E_(Mn)^(@)+4|""_(Mn)+2` = 1.2 V, then `E_(Mn)^(@)+7|""_(Mn)+4` is

Options

A. A) `0.3 V`
B. B) `0.1 V`
C. C) `1.7 V`
D. D) `2.1 V`

Answer

C

Explanation

(c): `Mn^(7+)+5e^(-) to Mn^(2+) , E^(@)` = 1.5 V
`DeltaG_(1)^(@) = -nFE^(@) = -5 xx F xx 1.5 rArr -7.5` F ...(i)
`Mn^(4+) + 2e^(-) to Mn^(2+), E^(@) = 1.2` V
`DeltaG_(2)^(@) = -nFE^(@) = -2xxFxx1.2 = -2.4` F ...(ii)
On subtracting eqn (ii) from (i), we get,
`Mn^(7+) + 3e^(-) to Mn^(4+), E^(@) =` ?
`DeltaG_(3)^(@) = DeltaG_(1)^(@) - DeltaG_(2)^(@)`
`-3FE^(@) = -7.5 F-(-2.4 F) rArr -3FE^(@) = -5.1 F`
`:. E^(@)` = 1.7 V