What is the number of elements in the `3^(rd)` period of the modern periodic table ?

Explanation

To find the number of elements in the 3rd period of the modern periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of the Periodic Table**: The periodic table is organized into periods (horizontal rows) and groups (vertical columns). Each period corresponds to the filling of electron shells.

2. **Identify the 3rd Period**: The 3rd period consists of the elements that fill the third electron shell (n=3).

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