In Bohr’s model, if the atomic radius of the first orbit is $r_0$ , then the radius of the fourth orbit is

$r_0$ 4$r_0$ $r_0$/16 16$r_0$

16$r_0$

$r_n \propto n^2 \Rightarrow \frac{r_4}{r_1}=\left(\frac{4}{1}\right)^2=\frac{16}{1} \Rightarrow r_4=16 r_1 \Rightarrow r_4=16 r_0$