Chemistry

Question Analysis
This question involves identifying the Group 1 element with the lowest first ionization energy. The main focus is on applying the basic group trend for ionization energy.

Key Concept Explanation
For elements in the same main group, ionization energy decreases as you move down the group.
Group 1 elements (alkali metals) follow this trend: the lower the element in the group, the larger its atomic radius, and the easier it is to remove its single valence electron.

Step-by-Step Solution
1. All options are in Group 1 (alkali metals).
2. Their positions from top to bottom: Li → Na → K → Cs.
3. Apply the group trend: ionization energy decreases down the grou...