Electron affinity is the amount of energy released when an electron is added to a neutral atom in the gaseous state to form an ion. It is a measure of the attraction of an atom for an added electron.

Generally, when moving from top to bottom in a group in the periodic table, the electron affinity decreases. This decrease is mainly because the atomic radius increases, which results in the added electron being farther from the atom's nucleus. A longer distance weakens the attraction between the electron and the nucleus.

In the case of halogens (Group 17 in the periodic table), the electron affinities are high because these atoms need just one more electron to complete their outer electron shell, achieving a stable noble gas configuration. Looking at fluorine (F), chlorine (Cl), and bromine (Br), we can analyze their trends in electron affinity.

Fluorine, being at the top of the halogens in the periodic table, might be expected to have the highest electron affinity. However, due to its very small size and high electron density, there is significant electron-electron repulsion when an extra electron is added. This repulsion somewhat diminishes the energy release upon gaining an electron.

Chlorine, on the other hand, while larger than fluorine, experiences lesser electron-electron repulsion relative to its size. This optimal balance leads to a generally higher amount of energy released when an electron is added to chlorine compared to fluorine and bromine. Therefore, chlorine often has a higher electron affinity than fluorine.

Bromine, being larger than both fluorine and chlorine, has an even smaller electron affinity because the added electron is further from the nucleus, reducing the effective nuclear charge experienced by the electron and consequently the energy release upon electron capture.

Thus, the typical order for electron affinities in these halogens would be $$Cl > F > Br$$. Therefore, the statement in the question, "The decreasing order of electron affinity of F, Cl, Br is F > Cl > Br" is actually FALSE. The correct order, as explained, should ideally be $$Cl > F > Br$$.