Three elements with filled outermost shell.

Explanation

To answer the question about three elements with filled outermost shells, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Concept of Filled Outermost Shell**:
- An element has a filled outermost shell when its outermost energy level (or shell) is completely occupied by electrons. This typically corresponds to having a full octet (8 electrons) or a full duplet (2 electrons for the first shell).

2. **Identifying the Group in the Periodic Table**:
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