The electron affinity of Cl when 1.0g of Cl atom is converted to Cl- (g) liberate 9.83 kJ energy is:

Cl(g)+1e−⟶Cl−(g)1g of Cl-atoms liberate energy                =9.83 kJ∴35.5g of Cl-atoms liberate energy               =9.83×35.5=349kJ∴ Electron affinity of Cl                    =−349 kJ