A) \[-\,0.260\,V\]
B) \[0.3394\,V\]
C) \[-0.3394\,V\]
D) \[+\,0.2606\,V\]
Correct Answer: D
Solution :
\[Cr\xrightarrow{{}}C{{r}^{3+}}+3{{e}^{-}}\] ?(i) \[F{{e}^{2+}}+2{{e}^{-}}\xrightarrow{{}}Fe\] ?(ii) Multiply Eq. (i) by 2 and Eq. (ii) by 3 \[\begin{align} & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,2Cr\xrightarrow{{}}2C{{r}^{3+}}+6{{e}^{-}} \\ & \underline{3F{{e}^{2+}}+6{{e}^{-}}\xrightarrow{{}}3Fe} \\ & 2Cr+3F{{e}^{2+}}\xrightarrow{{}}2C{{r}^{3+}}+3Fe \\ & n=6 \\ \end{align}\] From Nernst equation, \[{{E}_{cell}}=E_{cell}^{{}^\circ }-\frac{0.059}{n}\log \frac{{{[C{{r}^{3+}}]}^{2}}}{{{[F{{e}^{2+}}]}^{3}}}\] \[=[-\,0.44+0.74]-\frac{0.059}{6}\times \log \frac{{{(0.2)}^{2}}}{{{(0.02)}^{3}}}\] \[=0.3-0.0394=0.2603\,V\]
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