The question asks which element has the maximum photoelectric effect among Li, Na, K, and Cs. To answer this, we need to understand the concept of the photoelectric effect.
The photoelectric effect refers to the emission of electrons from a material when it is exposed to light. The ease with which electrons are emitted is influenced by the work function or ionization energy of the element. The lower the work function, the easier it is for electrons to be emitted when light is shone on the material.
Let's consider the given options:
The key concept is that alkali metals (group 1 elements) generally exhibit photoelectric effects quite readily due to their low ionization energies, and among the alkali metals, Cesium (Cs) has the lowest ionization energy. This implies that cesium can release electrons more easily when exposed to light compared to lithium (Li), sodium (Na), and potassium (K).
Therefore, due to its low ionization energy, Cesium (Cs) has the maximum photoelectric effect among the listed options.
Conclusion: The element with the maximum photoelectric effect is Cs (Cesium).