The metal used in solar cells is
Cesium
Explanation for correct option:
A. Cesium
Solar cell:
Explanation for incorrect options:
Metals such as tin, gold, and sodium are not used in solar cells due to their high ionization energies also these metals do not hold the property of converting sunlight into electrical energy. Thus options B, C, and D are incorrect.
Hence, the correct option is A i.e. Cesium.