Among the elements of the third period (Na to Ar), pick out the element
that is the most reactive metal.

Explanation

To determine the most reactive metal among the elements of the third period (from Sodium to Argon), we can follow these steps:

### Step 1: Identify the Elements in the Third Period
The elements in the third period of the periodic table are:
- Sodium (Na)
- Magnesium (Mg)
- Aluminum (Al)
- Silicon (Si)
...