The first use of quantum theory to explain the structure of the atom was made by

$A$ surface ejects electrons when hit by green light but not when hit by yellow light. Will electrons be ejected if the surface is hit by red light?

The radius of the first excited state of a Helium ion $(He^+)$ is given by (where $a_0$ is the radius of the first stationary state of the hydrogen atom):

When an electron in a hydrogen atom jumps from an infinite state to the first stationary state,the wavelength of the emitted radiation will be ...... (Rydberg constant = $1.097 \times 10^7 \ m^{-1}$):

When a certain metal was irradiated with light of frequency $4.0 \times 10^{16} \ s^{-1}$,the photoelectrons emitted had four times the kinetic energy as the kinetic energy of photoelectrons emitted when the same metal was irradiated with light of frequency $2.0 \times 10^{16} \ s^{-1}$. The threshold frequency $(v_0)$ of the metal in $s^{-1}$ is

The $Bohr$ model of an atom could not account for: