Radius of the nth orbit for hydrogen, r_{n}=\frac{\varepsilon _{0}h^{2}n^{2} }{\pi mq^{2} }

=\frac{(8.854\times 10^{-12})(6.62\times 10^{-34} )^{2}n^{2} }{\pi (9.1\times 10^{-31} )(1.6\times 10^{-19} )^{2}}

Therefore, the radius of the first orbit is,r_{1}=5.27\times 10^{-11} \times 1^{2}m

=5.27\times 10^{-11}m=0.527A.U.

The radius of the second orbit is,              r_{2}=5.27\times 10^{-11} \times 2^{2}=2.108A.U.

The radius of the third orbit is,                  r_{3}=5.27\times 10^{-11} \times 3^{2}=4.743A.U.