In the Bohr series of lines of the hydrogen spectrum,the third line from the red end corresponds to which one of the following inter-orbit jumps of the electron for Bohr orbits in an atom of hydrogen?

When an electron with energy $10.8 \,eV$ collides with a hydrogen $(H)$ atom,what will happen?

In a mixture of $H$ and $He^{+}$ gases,all $H$ atoms and $He^{+}$ ions are excited to their first excited states. Subsequently,on de-excitation in $H$ atoms,energy is transferred to the excited $He^{+}$ ion. The quantum number $n$ of the $He^{+}$ ion after the energy is transferred is:

Which of the following transitions will emit the shortest wavelength?

The ground state energy of $H$ is equal to

The ratio of the time period of an electron in the first and third orbit of an $H$-atom would be: