What is the trend down the group in the periodic table of atomic size ?

Explanation

### Step-by-Step Solution:

1. **Understanding Atomic Size**: Atomic size or atomic radius refers to the distance from the nucleus of an atom to the outermost shell of electrons.

2. **Trend Down the Group**: As we move down a group in the periodic table, the atomic size increases. This is a general trend observed in the periodic table.

3. **Reason for the Increase**: The increase in atomic size down a group is primarily due to the addition of new electron shells. Each element in a group has one more electron shell than the element above it.

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