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.
Above the minimum frequency, energy depends on the frequency of the light, not on the intensity of the light.
