Question -
Answer -
Allthe three, lithium, potassium, and cesium, are alkali metals. Still, K and Csare used in the photoelectric cell and not Li.
Thisis because as compared to Cs and K, Li is smaller in size and therefore,requires high energy to lose an electron. While on the other hand, K and Cshave low ionization energy. Hence, they can easily lose electrons. Thisproperty of K and Cs is utilized in photoelectric cells.