The longest wavelength of the Lyman series for hydrogen atom is the same as the wavelength of a certain line in the spectrum of `He^+` when the electron makes a trensiton from `n rarr 2`. The value of n is

Options

A. 3
B. 4
C. 5
D. 6

Answer

B

Explanation

Longest wavelength of Lyman series means,
minimum energy corresponding n =2 to n=1.
`:. (E_2 - E_1)_H = (E_n - E_2)_(He+)`
`:. (-13.6)/((2))^2 +(13.6)/((1))^2 = (-13.6(Z)^2/(n^2 + (13.6(Z)^2/((2))^2`
Putting Z =2, we get n =4.