Chemistry

Question Analysis
This question involves ordering elements in the same group by atomic radius from largest to smallest.
The main focus is on applying the group trend of atomic radius.

Key Concept Explanation
Atomic radius increases down a group because each element has an additional electron shell.
Thus, the radius order for Group 2 elements (alkaline earth metals) is: Ba (Period 6) > Sr (Period 5) > Ca (Period 4) > Mg (Period 3).

Step-by-Step Solution
1. Identify the group: Ba, Sr, Ca, Mg are all in Group 2.
2. Recall the group trend: Atomic radius increases from top to bottom of a group.
3. List the elements by period (from highes...