65. If \( a _{0} \) is denoted as the Bohr radius of hydrogen atom, then what is the de-Broglie wavelength ( \( \lambda \) ) of the electron present in the second orbit of hydrogen atom? [ n : any integer]
(1) \( \frac{2 a_{0}}{n \pi} \)
(2) \( \frac{8 \pi a_{0}}{n} \)
(3) \( \frac{4 \pi a_{0}}{n} \)
(4) \( \frac{4 n}{\pi a_{0}} \)
Ans. (2)