Introduction:
The photoelectric effect refers to the phenomenon where electrons are emitted from a material's surface when it is exposed to light of a certain frequency. The energy required to remove an electron from the material is known as the work function. The retarding potential is the minimum negative potential that needs to be applied to stop the emitted electrons from reaching the anode in a photoelectric cell.

Explanation:
When light of a specific frequency (greater than or equal to the threshold frequency) is incident on a material's surface, electrons are emitted due to the absorption of photons. The energy of each photon is given by the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency of the light. The energy required to remove an electron from the material's surface is given by the work function, denoted as φ.

Relationship between Retarding Potential and Frequency:
The retarding potential is the negative potential that needs to be applied to stop the emitted electrons from reaching the anode. It is given by the equation eV = hf - φ, where e is the charge of an electron and V is the retarding potential. Rearranging the equation, we can express V as V = (1/e)(hf - φ).

As the frequency of the incident light increases, the energy of each photon (hf) also increases. Given that the work function, φ, remains constant for a specific material, the term hf - φ also increases. Consequently, the retarding potential V increases as well. This implies that a higher potential difference is required to stop the more energetic electrons from reaching the anode.

Therefore, the correct answer is option 'D' - the retarding potential increases with the frequency of light causing the photoelectric effect.

Summary:
In the photoelectric effect, the retarding potential is the minimum negative potential required to stop the emitted electrons from reaching the anode. As the frequency of the incident light increases, the energy of the photons increases, resulting in a higher retarding potential. This is because more energy is needed to counteract the more energetic electrons emitted from the material's surface.