The conductivity of a solution of concentration $0.1 \mathrm{~mol} \mathrm{~L}^{-1}$ of a weak monobasic acid $(\mathrm{HA})$ (in $\mathrm{S} \mathrm{cm}^{-1}$ ) is (Given : $\Lambda^{\circ}{ }_{\mathrm{HA}}=400 \mathrm{Scm}^2 \mathrm{~mol}^{-1}$ and degree of dissociation ( $\alpha$ ) of $\mathrm{H} A=0.02$ )

At 300 K , the conductivity of $0.01 \mathrm{~mol} \mathrm{dm}^{-3}$ aqueous solution of acetic acid is $19.5 \times 10^{-5} \mathrm{mho} \mathrm{cm}^{-1}$ and limiting molar conductivity of acetic acid at the same temperature is $390 \mathrm{mho} \mathrm{cm}^2 \mathrm{~mol}^{-1}$. The degree of dissociation of acetic acid is

The $E^{\circ}$ of $\mathrm{Ce}^{4+} / \mathrm{Ce}^{3+}=1.6 \mathrm{~V}, \mathrm{Fe}^{3+} / \mathrm{Fe}^{2+}=0.76 \mathrm{~V}$ the $E^{\circ}$ of $\mathrm{Fe}^{3+}$ oxidising $\mathrm{Ce}^{3+}$ is