According to classical theory, the circular path of an electron in Rutherford atom is

The following diagram indicates the energy levels of a certain atom when the system moves from $2E$ level to $E$, emitting a photon of wavelength $\lambda $. The wavelength of photon produced during its transition from $\frac{4E}{3}$ level to $E$ is

According to the nuclear model of an atom, what is the area of the whole mass of the atom located ?

Explain the Rutherford atomic model and its limitation.

The possible quantum number for $3d$ electron are

Hydrogen atom is excited from ground state to another state with principal quantum number equal to $4$. Then the number of spectral lines in the emission spectra will be