If the radius of the first orbit of hydrogen atom is a0, then de Broglie's wavelength of electron in 3rd orbit is [2023]
(4)
rn=a0×n2, for 3rd orbit r3=9a0
mV=3h2πr3=3h2π9a0=h6πa0
and λ=hmV=hh6πa0=6πa0