$(a)\;r=(\large\frac{n^2 h^2}{82 a m \pi^{2}})^{\large\frac{1}{4}}\qquad(b)\;r=(\large\frac{n^2 h^2}{4 a m \pi^{2}})^{\large\frac{1}{4}}\qquad(c)\;r=(\large\frac{n^2 h^2}{8 a m \pi^{2}})^{\large\frac{1}{4}}\qquad(d)\;r=(\large\frac{n^2 h^2}{16 a m \pi^{2}})^{\large\frac{1}{4}}$