$\mathrm{Zn} \longrightarrow \mathrm{Zn}^{2+}+2 \mathrm{e}^{-}$ 

$2 \mathrm{Fe}^{3+}+2 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Fe}^{2+}$ 

$\mathrm{Zn}+2 \mathrm{Fe}^{3+} \longrightarrow \mathrm{Zn}^{2+}+2 \mathrm{Fe}^{2+}$ 

$\mathrm{E}_{\mathrm{cell}}^0=0.77-(-0.76)$ 

$=1.53 \mathrm{~V}$ 

$1.50=1.53-\frac{0.06}{2} \log \left(\frac{\mathrm{Fe}^{2+}}{\mathrm{Fe}^{3+}}\right)^2$ 

$\log \left(\frac{\mathrm{Fe}^{2+}}{\mathrm{Fe}^{3+}}\right)=\frac{0.03}{0.06}=\frac{1}{2}$ 

$\frac{\left[\mathrm{Fe}^{2+}\right]}{\left[\mathrm{Fe}^{3+}\right]}=10^{1 / 2}=\sqrt{10}$ 

$\frac{\left[\mathrm{Fe}^{3+}\right]}{\left[\mathrm{Fe}^{2+}\right]}=\frac{1}{\sqrt{10}}$ 

$\frac{\left[\mathrm{Fe}^{3+}\right]}{\left[\mathrm{Fe}^{2+}\right]+\left[\mathrm{Fe}^{3+}\right]}=\frac{1}{1+\sqrt{10}}=\frac{1}{4.16}$ 

$=0.2402$ 

$=24 \times 10^{-2}$