Number of spectral lines obtained in $He^{+}$ spectra,when an electron makes transition from fifth excited state to first excited state will be

Radius of $1^{st}$ orbit of $H$ and some orbit of $Be^{3+}$ is same. Energy of their orbit of $Be^{3+}$ is ............$eV$.

In Rutherford's experiment,generally the thin foil of heavy atoms,like gold,platinum etc. have been used to be bombarded by the $\alpha$-particles. If the thin foil of light atoms like Aluminium etc. is used,what difference would be observed from the above results?

The limiting line in the Balmer series of the $H$ spectrum has a frequency of ....... $(R_\infty = 3.29 \times 10^{15} \, cycles/s)$

The four lowest energy levels of the $H$ atom are shown in the figure. The number of emission lines will be ...... .

Two series of spectral lines of atomic hydrogen which do not belong to the infrared spectral region are