$(a)\;\large\frac{\varepsilon_{0} n^2 h^2}{2 \pi m_{e} e^2}\qquad(b)\;\large\frac{\varepsilon_{0} n^2 h^2}{4 \pi m_{e}e^2} \qquad(c)\;\large\frac{\varepsilon_{0} n^2 h^2}{8 \pi m_{e}e^2} \qquad(d)\;\large\frac{\varepsilon_{0} n^2 h^2}{624 \pi m_{e}e^2} $