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 (Na to Ar), we can follow these steps:

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