The spectrum of helium is similar to which of the following?

In the Balmer series of the hydrogen atom spectrum,which electronic transition causes the third line?

If the work function of a metal is $6.63 \times 10^{-19} \ J$,the maximum wavelength of the photon required to remove a photoelectron from the metal is $.... \ nm$. (Nearest integer)
[Given : $h = 6.63 \times 10^{-34} \ J \ s$,and $c = 3 \times 10^{8} \ m \ s^{-1}$ ]

The wavelength of a spectral line emitted is inversely proportional to:

Calculate the wavenumber of the photon emitted during transition from the orbit of $n=2$ to $n=1$ in a hydrogen atom. $[R_H = 109677 \ cm^{-1}]$ (in $cm^{-1}$)

Bohr's atomic model explains the spectrum of only $.......$.