Circumference of Bhor$\text{'}$s atomic orbit is related to De-Broglie wave  length $\left(\lambda \right)$ is as given below$2\mathrm{\pi }\mathrm{ }{\mathrm{r}}_{\mathrm{n}}=\mathrm{n}\mathrm{\lambda }$

n$=$ Orbit number

n$=$$4$

r_n $=$ radius of the n^th orbit

r_n $=$ 0.864 nm$\Rightarrow \mathrm{ }\mathrm{\lambda }=\frac{2\mathrm{\pi }\mathrm{ }{\mathrm{r}}_{\mathrm{n}}}{\mathrm{n}}=\frac{2\times 3.14\times 0.864}{4}\mathrm{ }\mathrm{n}\mathrm{m}$
$=\mathrm{ }1.3565\mathrm{ }\mathrm{n}\mathrm{m}$