Home/
Competitive Exams/
JEE Main & Advanced/
Chemistry/
Periodic Table and Periodicity/
Question 840004
JEE Chemistry · Medium

Periodic Table and Periodicity: Ionisation energy MCQ

Solve this quality-checked JEE multiple-choice question, then review the correct answer and explanation.

Timer-based practiceDetailed answer reviewMobile-friendly flow
Ionisation energyMediumQuestion 840004

Question

The first ionisation energy (IE₁) generally increases:
  1. A
    Across a period and up a group
    Correct
  2. B
    Down a group and across a period
  3. C
    Only down a group
  4. D
    Only across a period

Correct answer

Across a period and up a group

Explanation

IE₁ increases: (1) across a period — higher Zeff, smaller radius; (2) up a group — smaller atoms, valence electrons closer to nucleus. Exceptions: Group 13 (IE < Group 2 due to 2p vs 2s), Group 16 (IE < Group 15 due to e⁻-e⁻ repulsion in paired orbital).

Review Periodic Table and Periodicity notesStart timed chapter practice