Calculate the energy in $\mathrm{kJ} \mathrm{mol}^{-1}$ required to separate a positive and negative charge from $0.3 \mathrm{nm}$ to infinity in $(a)$ a vacuum,
(b) a solvent of dielectric constant $10,$ and
(c) water at $25^{\circ} \mathrm{C},$ which has a dielectric constant of approximately 80