Chemistry

Question Analysis
This question evaluates the student's ability to arrange elements in order of decreasing atomic radius and explain the reasoning based on their position in the periodic table.

Key Concept Explanation
The atomic radius generally increases as you move down a group due to the addition of new electron shells, which increases the distance between the nucleus and the outermost electrons.

Step-by-step Solution
1. Identify the elements: Strontium (Sr), Calcium (Ca), Magnesium (Mg), and Beryllium (Be) are in Group 2 (alkaline earth metals).
2. Arrange the elements in order of decreasing atomic radius: Sr > Ca > Mg > Be.
3. Explain the reasoning: All these elements are in the same group, and the atomic radius generally increases as you move down a group. The addition of new electron shells as you move down the group increases the distance between the nucleus and the outermost electrons, leading to a larger atomic radius.
4. Therefore, the correct answer is: The ele...