Q.

If the radius of the first orbit of hydrogen atom is a0, then de Broglie's wavelength of electron in 3rd orbit is          [2023]

1 πa03  
2 πa06  
3 3πa0  
4 6πa0  

Ans.

(4)

rn=a0×n2, for 3rd orbit r3=9a0

mV=3h2πr3=3h2π9a0=h6πa0

and λ=hmV=hh6πa0=6πa0