Arrange the following as per instructions given in the brackets:
Cl, F, Br, I (increasing order of electron affinity)

Answer

To arrange the elements Cl, F, Br, and I in increasing order of electron affinity, follow these steps:

### Step 1: Understand Electron Affinity
Electron affinity is the amount of energy released when an electron is added to a neutral atom in the gas phase. Generally, electron affinity increases across a period and decreases down a group in the periodic table.

**Hint:** Remember that electron affinity is influenced by atomic size and the effective nuclear charge.

### Step 2: Identify the Group and Period
All the elements given (Cl, F, Br, I) belong to Group 17 (the halogens) of the periodic table. As you move down the group from F to I, the atomic size increases because additional electron shells are added.

**Hint:** Group 17 elements have similar properties but differ in size and electron affinity.

### Step 3: Analyze the Trend in Electron Affinity
As you move down the group, the electron affinity generally decreases. This is because the increased distance between the nucleus and the added electron (due to larger atomic size) results in a weaker attraction, making it harder to add an electron.

**Hint:** Consider how atomic size affects the attraction between the nucleus and the added electron.

### Step 4: Consider the Exception of Chlorine and Fluorine
While the trend suggests that electron affinity decreases down the group, there is an exception between chlorine and fluorine. Chlorine has a higher electron affinity than fluorine due to the smaller size of the 2p orbital in fluorine, which leads to greater electron-electron repulsion when an additional electron is added.

**Hint:** Pay attention to the specific electron configurations of Cl and F to understand the exception.

### Step 5: Arrange the Elements
Based on the analysis:
- Iodine (I) has the lowest electron affinity.
- Bromine (Br) has a higher electron affinity than iodine but lower than chlorine.
- Fluorine (F) has a higher electron affinity than bromine, but lower than chlorine.
- Chlorine (Cl) has the highest electron affinity.

Thus, the increasing order of electron affinity is:
**I < Br < F < Cl**

**Final Answer:** Iodine (I), Bromine (Br), Fluorine (F), Chlorine (Cl).