According to Balmer formula

`bar(v)=1/lambda=R(1/n_(1)^(2)-1/n_(2)^(2))`

If wavelength `(lambda)` is to be longest, then energy and wave number `(bar(v))` must be minimum. For this `n_(2)` must be lowest.

`:. N_(1)=2, n_(2)=3` (Balmer Series)

`bar(v)=R_(H)(1/2^(2)-1/3^(2))`

`=R_(H)xx5/36`

`=109678xx5/36`

`=15233 cm^(-1)=15233xx10^(2) m^(-1)`

`=1.5233xx10^(6) m^(-1)`