Chemistry

Question Analysis
This question involves ordering elements by atomic radius within the same period.
The main focus is on applying the period trend of atomic radius.

Key Concept Explanation
Atomic radius decreases across a period (left to right) due to increasing nuclear charge.
Elements in Period 3 follow this trend: Na (Group 1) > Mg (Group 2) > Al (Group 13) > Si (Group 14).

Step-by-Step Solution
1. Identify the period: Na, Mg, Al, Si are all in Period 3.
2. Recall the period trend: Atomic radius decreases from left to right.
3. List the elements in order of increasing atomic number (left to right): Na, Mg, Al, ...