d
(d) \(mv{r_n} = \frac{{nh}}{{2\pi }} \Rightarrow p{r_n} = \frac{{nh}}{{2\pi }} \Rightarrow \frac{h}{\lambda } \times {r_n} = \frac{{nh}}{{2\pi }}\)
\( \Rightarrow \lambda = \frac{{2\pi {r_n}}}{n},\)for first orbit \(n = 1\) so \(\lambda = 2\pi {r_1}\)
= circumference of first orbit