The correct order for first ionization energy among the following is :

Question

Accepted Answer

The correct order for first ionization energy among the elements given is $F > N > O > C$, as stated in Option 4. Let's provide a detailed explanation to justify why this order is correct and why the other options are incorrect.

1. **Explanation for Option 4 ($F > N > O > C$):**
   - **Fluorine (F):** Fluorine has the highest first ionization energy among the elements listed. This is because it is the most electronegative element, with a strong attraction for electrons due to its small atomic size and high effective nuclear charge.
   - **Nitrogen (N):** Nitrogen has a higher first ionization energy than oxygen. This is due to its half-filled p-orbital configuration (2p³), which is relatively stable. Removing an electron from this stable configuration requires more energy.
   - **Oxygen (O):** Oxygen has a slightly lower first ionization energy than nitrogen. Although oxygen is more electronegative, the electron-electron repulsion in its 2p⁴ configuration makes it easier to remove an electron compared to nitrogen.
   - **Carbon (C):** Carbon has the lowest first ionization energy among these elements. Its 2p² configuration is less stable compared to the half-filled configuration of nitrogen, making it easier to remove an electron.

2. **Why the other options are incorrect:**
   - **Option 1 ($C > N > O > F$):** This order is incorrect because carbon cannot have a higher ionization energy than nitrogen, oxygen, or fluorine. Carbon's lower effective nuclear charge and larger atomic radius compared to these elements result in a lower ionization energy.
   - **Option 2 ($O > N > F > C$):** This order incorrectly places oxygen before nitrogen and fluorine. As explained, nitrogen's half-filled p-orbital makes its ionization energy higher than oxygen's, and fluorine, being the most electronegative, should have the highest ionization energy.
   - **Option 3 ($O > F > N > C$):** This order incorrectly places oxygen before fluorine and nitrogen. Fluorine should have the highest ionization energy due to its high electronegativity, and nitrogen should have a higher ionization energy than oxygen due to its stable half-filled configuration.

In conclusion, Option 4 ($F > N > O > C$) is the correct order for first ionization energy among the given elements, based on their electronic configurations and the factors affecting ionization energy.