When an electron in a hydrogen spectrum transitions from the $7^{th}$ energy level to the $1^{st}$ energy level,what is the total number of spectral lines produced?

The separation energy of the electron present in the shell $n = 3$ is $1.51 \ eV$. What is the energy in the first excited state? ............ $eV$

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?

Total number of spectral lines when an electron jumps from the $8^{th}$ orbit to the $2^{nd}$ orbit is:

The ionisation energy of a certain element is $1540 \ kJ \ mol^{-1}$. When the atoms of this element are in the first excited state,the ionisation energy is only $300 \ kJ \ mol^{-1}$. Determine the region of the electromagnetic wave spectrum in which the light is emitted during a transition from the first excited state to the ground state.

Which of the following energy changes is less than the third Balmer transition in the $He^{\oplus}$ ion?