Arrange the following elements in order of decreasing electron affinity: F, Cl, Br, I.
Electron affinity decreases down group 17, with Cl highest due to optimal size and nuclear charge, followed by F (anomaly due to repulsion). Order: Cl > F > Br > I.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electron Gain Enthalpy and Electronegativity and Valency