What transition in `He^(o+)` ion shall have the same wave number as the first line in Balmer series of H atom ?

Options

A. `3rarr 2`
B. `6 rarr4`
C. `5rarr3`
D. `7rarr5`

Answer

B

Explanation

` E_(3) - E_(2) ` for ` H= - E_(1H)/(9) + E_(1H)/(4) = (5 E_1H)/(36)`
` [because E_n = E_(1H)/(n^(2))]`
` E_6 - E_4 or He^+ = [ - ( E_(1H) xx 2^2 )/6^2 + (E_(1H) xx 2^(2))/4^2 ]`
`:. E_(nHe^+) = (E_(1H)xx Z^2)/n^2 = + (5E_(1H))/( 36)`.