Question

In which of the following, elements are correctly arranged in the decreasing order of their second ionization enthalpies?

• A. O > F > N > C
• B. N > O > F > C
• C. F > O > N > C
• D. C > N > O > F

Hint:

Second ionization enthalpy depends on effective nuclear charge and atomic size. Across a period, it generally increases from left to right.

Answer 1

The Correct Option is A

Step 1: Write the +1 ion configurations.
O\(^+\): [He]2s\(^2\)2p\(^3\) (half-filled, stable), F\(^+\): [He]2s\(^2\)2p\(^4\), N\(^+\): [He]2s\(^2\)2p\(^2\), C\(^+\): [He]2s\(^2\)2p\(^1\).

Step 2: Rank by difficulty of removing the next electron.
O\(^+\) has a half-filled 2p shell -- extra stable, so its 2nd IE is highest. F\(^+\) loses from a paired 2p (easier than half-filled). N\(^+\) and C\(^+\) have fewer p-electrons. Order: O \(>\) F \(>\) N \(>\) C.
\[ \boxed{O > F > N > C} \]