Ionization Energy Trends in Periodic Table

Steps:

• Recall ionization energy is energy required to remove an electron from a gaseous atom.
• Analyze vertical trends: down a group, atomic size increases, shielding effect rises, reducing attraction to nucleus.
• Analyze horizontal trends: across a period, nuclear charge increases, pulling electrons closer, raising ionization energy.
• Evaluate each statement against these trends for Group 2 (alkaline earth metals) and Period 3.

Why B is correct:

• Down Group 2, atomic radius increases and inner electrons shield outer ones, decreasing effective nuclear charge and thus ionization energy.

Why the others are wrong:

• A: Ionization always requires energy input, so endothermic, but statement implies exceptions—it's universally endothermic.
• C: Across Period 3, ionization energy generally increases due to higher nuclear charge with similar shielding.

Final answer: B