Cl>F>Br>I>At
As atomic radius increases down the group,electron affinity decreases
Fluorine is exception due to its small size it cannot release high amount of energy

Decreasing Order of Electron Affinity of Halogens

The electron affinity of an element refers to the energy change that occurs when an electron is added to a neutral atom to form a negative ion. In the case of halogens, electron affinity measures their ability to accept an additional electron and form a halide ion.

The decreasing order of electron affinity of halogens is as follows:

1. Chlorine (Cl)
2. Fluorine (F)
3. Bromine (Br)
4. Iodine (I)
5. Astatine (At)

Explanation:

1. Chlorine (Cl)
Chlorine has the highest electron affinity among the halogens. This is because it has a small atomic radius and a high effective nuclear charge, which means that the attraction between the nucleus and the incoming electron is strong. As a result, chlorine readily accepts an additional electron to achieve a stable electron configuration.

2. Fluorine (F)
Fluorine has the second highest electron affinity among the halogens. It is the smallest halogen atom with the highest effective nuclear charge. The small atomic size and high nuclear charge make fluorine highly electronegative. Therefore, it has a strong attraction for an additional electron.

3. Bromine (Br)
Bromine has a lower electron affinity compared to chlorine and fluorine. It has a larger atomic size and a lower effective nuclear charge. The increase in atomic size reduces the attraction between the nucleus and the incoming electron, resulting in a lower electron affinity.

4. Iodine (I)
Iodine has an even larger atomic size and a lower effective nuclear charge than bromine. The larger atomic size leads to weaker attraction between the nucleus and the incoming electron. Hence, iodine has a lower electron affinity compared to bromine.

5. Astatine (At)
Astatine has the lowest electron affinity among the halogens. It has the largest atomic size and the lowest effective nuclear charge. The large atomic size and weak nuclear charge make it less likely for astatine to accept an additional electron, resulting in the lowest electron affinity among the halogens.

In conclusion, the decreasing order of electron affinity of halogens is chlorine (Cl) > fluorine (F) > bromine (Br) > iodine (I) > astatine (At). The trend is primarily influenced by the atomic size and effective nuclear charge of the halogen atoms.