Chemistry

Question Analysis
This question tests the understanding of periodic trends in atomic radius, specifically across a period.

Key Concept Explanation
Atomic radius decreases as you move from left to right across a period due to the increasing nuclear charge, which pulls the valence electrons closer to the nucleus.

Step-by-step Solution
1. Identify the period and group of each element: Rubidium (Rb) is in Group 1, Strontium (Sr) is in Group 2, Yttrium (Y) is in Group 3, and Zirconium (Zr) is in Group 4.
2. Compare the elements across Period 5: Rb (Group 1) > Sr (Group 2) ...