The energy required to excite an electron from the first orbit to the third orbit in a hydrogen atom is .......... $eV$.

Positronium consists of an electron and a positron (a particle which has the same mass as an electron,but opposite charge) orbiting round their common centre of mass. Calculate the value of the Rydberg constant for this system.

Which transition in a $H$ atom emits the maximum energy?

If the electron jumps from $7.00 \ eV$ energy level to $5.0 \ eV$ energy level,it :

If the shortest wavelength in the Lyman series of a hydrogen atom is $A$,then the longest wavelength in the Paschen series of $He^{+}$ is:

The spectrum of $Li^{2+}$ is similar to that of: