Calculate the iongest wavelength transition in the paseches series of `He^(o+)`.

Explanation

`bar v = R_(H) xx Z6*(2) [(1)/(n_(1)^(2)) - (1)/(n_(2)^(2))]`
For He `Z = 2` For paschen series , `n_(1) = 3` For the longest wavelength, `n_(2) = 4`
`(1)/(lambda) = 109678 xx (2)^(2) xx [(1)/(3^(2)) - (1)/(4^(2))]`
`= 10978 xx 4 xx [(1)/(9) - (1)/(16)]`
`= 109678 xx 4 xx (7)/(144)`
`or lambda = 4589 Å`