A. Photoelectric effect
B. Compton Effect
C. Pair production
D. None of these
A. Photoelectric effect
A photocell works on the principle of the A. Photoelectric effect.
The photoelectric effect describes the phenomenon where light striking a material can eject electrons from that material. In a photocell, this principle is used to convert light energy into electrical energy.
Compton Effect, Pair Production, and other options you provided are different ways light interacts with matter, but they are not the primary working principle behind photocells.