Electron gain enthalpy values of the elements are given below in kJ/mol,
F−333Cl−349 Te −190 Po −174.
Down the group electron affinity decreases. The size of fluorine atom is small. The addition of electron to small fluorine atom results in electron-electron repulsions. Hence, fluorine has less electron affinity than chlorine.
Hence, the correct order is
Cl>F>Te>PO