The period of revolution of an electron revolving in $n^{th}$ orbit of $H$-atom is proportional to

In Bohr's atomic model, the energy of the electron is $E$ in the second orbit of a hydrogen atom. The energy of the electron in the third orbit of a helium atom $(Z = 2)$ will be:

In the Bohr model of a hydrogen atom,the electrostatic force on the electron depends on the principal quantum number $n$ as:

The electron in a hydrogen atom makes a transition $n_1 \rightarrow n_2$,where $n_1$ and $n_2$ are the principal quantum numbers of the two states. Assume the Bohr model to be valid. The frequency of orbital motion of the electron in the initial state is $1/27$ of that in the final state. The possible values of $n_1$ and $n_2$ are

The total energy of an electron $E_n = -\frac{Z^2me^4}{8\epsilon_0^2n^2h^2}$ in an atom is based on which hypothesis? Under what condition is this formula true?

Monochromatic radiation of wavelength $\lambda$ is incident on a hydrogen sample containing atoms in the ground state. Hydrogen atoms absorb the light and subsequently emit radiations of ten different wavelengths. The value of $\lambda$ is.....$nm$.