Question
The correct order of C , N , O and F in terms of second ionisation potential is
JEE Main
Chemistry
Classification of Elements and Periodicity in Properties
2026
JEE Main 2026 (24 January Shift 2)
JEE Main Chemistry Question (2026) — Solution
Options
- A. C < N < F < O
- B. C < O < N < F
- C. C < F < N < O
- D. F < N < C < O
Answer
A. C < N < F < O
Step-by-step solution
Second ionization potential (I₂) is the energy to remove the second electron. After removing the first electron: C⁺ has 2p¹, N⁺ has 2p², O⁺ has 2p³ (half-filled, stable), F⁺ has 2p⁴. C has lowest I₂ as 2p electrons are least tightly bound with lowest nuclear charge. N has slightly higher I₂ than C due to increased nuclear charge. F has highest I₂ due to highest effective nuclear charge. O⁺ with half-filled 2p is relatively stable, making I₂ of O intermediate. Order: C < N < F < O
Related: Chemistry — Classification of Elements and Periodicity in Properties · All PYQ Banks