Arrange the following elements in increasing order of their atomic radii.
Cl, At, Br I

Explanation

To arrange the elements Cl (Chlorine), At (Astatine), Br (Bromine), and I (Iodine) in increasing order of their atomic radii, we need to understand how atomic radii change within a group of the periodic table.

### Step-by-Step Solution:

1. **Identify the Group**: All four elements (Cl, Br, I, At) belong to Group 17 (the halogens) of the periodic table.

2. **Understand Atomic Radii Trend in a Group**: In a group, as you move down the periodic table, the atomic radius increases. This is because with each successive element, an additional electron shell is added, which increases the distance between the outermost electrons and the nucleus.

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