The correct order of the atomic radii of C, Cs, Al, and S is:

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Strategy:
 Use both group and period trends to rank atomic size. Atomic radius increases significantly down groups and decreases across periods.

Step 1: Locate elements
-  (, Per 2)  Period 2. Smallest.
-  (, Per 3)  Period 3. Group 13.
-  (, Per 3)  Period 3. Group 16.
-  (, Per 6)  Period 6. Group 1. Largest.

Step 2: Comparison in Period 3
Across Period 3: . So  is larger than .

Step 3: Final Order

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