Chemistry

Question Analysis
This question tests the understanding of the reason behind the increase in atomic radius as you move down a group in the periodic table.

Key Concept Explanation
As you move down a group, the addition of new electron shells (higher principal quantum number n) leads to greater electron shielding, which outweighs the increased nuclear charge, resulting in an increase in atomic radius.

Step-by-step Solution
1. Identify the key concept: atomic radius increases down a group due to the addition of new electron shells.
2. Evaluate each option:
Option A: Incorrect, the number of protons increases, not decreases.
Option B: Correct, the number of electron shells increases, leading to greater electron shielding. This increase in shielding outweighs the effect of increasing nucl...