Among the following, number of metal/s which can be used as electrodes in the photoelectric cell is ______. (Integer answer)
(A) Li (B) Na (C) Rb (D) Cs

A photoelectric cell works on the principle of the photoelectric effect. For a metal to be used as an electrode in a photoelectric cell, it must have a sufficiently low work function (ionization energy) so that visible or near-ultraviolet light can eject electrons from its surface.

Among the alkali metals, the work functions decrease as we go down the group: Li (2.42 eV) $$>$$ Na (2.28 eV) $$>$$ Rb (2.09 eV) $$>$$ Cs (1.95 eV). While all alkali metals have relatively low ionization energies, cesium (Cs) has the lowest work function and is the most commonly used metal in photoelectric cells. It is sensitive to visible light and is the standard choice for practical photoelectric applications.

Lithium and sodium have work functions that are too high for efficient use in standard photoelectric cells operating with visible light. Rubidium, while having a low work function, is less commonly used compared to cesium. Among the given metals, only cesium is practically employed as an electrode in photoelectric cells.

Therefore, the number of metals that can be used as electrodes in a photoelectric cell is $$\boxed{1}$$.