$4\mathrm{.}5$ The mobility, $u_j,$ is related to the diffusion coefficient, $D_j,$ by $(4\mathrm{.}1\mathrm{.}11).$

a$)$ From the mobility data in Table $2\mathrm{.}3\mathrm{.}2,$ estimate the diffusion coefficients of $H^{+},I^{-},$ and $L{i}^{+}$at $25C.$

b$)$ Write the equation for the estimation of $D_j$ from the ${}_j-$value.