State variation in number of shells in Group

Explanation

### Step-by-Step Solution:

1. **Understanding Groups in the Periodic Table**:
- Groups are the vertical columns in the periodic table. Each group contains elements that have similar chemical properties.

2. **Identifying the Variation in Number of Shells**:
- As you move down a group in the periodic table, the number of electron shells increases. This is because each successive element has an additional electron shell compared to the one above it.

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