If the radius of second stationary orbit (in Bohr’s atom) is R. Then, radius of third orbit will be

r = $0.529\times \frac{{\mathrm{n}}^2}{\mathrm{z}}$

r $\mathrm{\alpha }$ n²

R ∝ (2)²                          .......(1)

R₁ ​∝ (3)²                           .......(2)

Divide (1) by (2)

$\frac{{\mathrm{R}}_1}{\mathrm{R}}=\frac{4}{9}$​​

R₁ ​= $\frac{9\mathrm{R}}{4}$​

R₁ ​= 2.25 R