Answer is: D) Light is emitted from an atom as an electron falls from an excited state to the ground state releasing a photon.
Electrons can jump from one energy level to another, absorbing or emitting electromagnetic radiation with a frequency ν (energy difference of the levels).
When electron jump from higher to lower energy level (shell), it emitting (releasing) energy.
For example, when the electron changes from n=4 (fouth shell) to n=2 (second shell), the photons are emitted.
Albert Einstein (1879-1955) proposed that a beam of light is a collection of discrete wave packets (photons) with energy hν, where h is Planck constant and ν is frequency.
The photons have a characteristic energy proportional to the frequency of the light.
Minimum frequency or the threshold frequency is energy below which no photoelectrons are emitted. Â
Above the minimum frequency, energy depends on the frequency of the light, not on the intensity of the light.