In a hydrogen atom,if an electron transitions from an $n$-th orbit to the ground state,and the total number of spectral lines observed is $10$,then the value of $n$ is:

The electrostatic force of attraction between the electron and the nucleus in a hydrogen atom is given by:

The energy of an electron in a hydrogen atom in its ground state is $-13.6 \ eV$. The energy of the level corresponding to the quantum number equal to $5$ is ............. $eV$.

In astronomical observations,signals observed from the distant stars are generally weak. If the photon detector receives a total of $3.15 \times 10^{-18} \, J$ from the radiations of $600 \, nm$,calculate the number of photons received by the detector.

The radius of the second Bohr orbit,in terms of the Bohr radius,$a_{0}$,in $Li^{2+}$ is

Give names of atomic models and write about Thomson model.