Question

Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: The first ionization enthalpy for oxygen is lower than that of nitrogen.
Reason R: The four electrons in 2p orbitals of oxygen experience more electron-electron repulsion.
In the light of the above statements, choose the correct answer from the options given below.

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Answer 1

The Correct Option is B

The given question involves understanding the concepts of ionization enthalpy and electron-electron repulsion in atomic orbitals. Here’s a step-by-step explanation of the given statements:

1. Assertion A: "The first ionization enthalpy for oxygen is lower than that of nitrogen."
   • Ionization enthalpy is the energy required to remove one mole of electrons from one mole of gaseous atoms. It is influenced by atomic size, nuclear charge, and electron-electron repulsions.
   • Nitrogen has the electronic configuration 1s² 2s² 2p³, with a half-filled stable p-orbital. Oxygen has the configuration 1s² 2s² 2p⁴.
   • The stability of half-filled orbitals makes nitrogen more resistant to losing an electron, thus having a higher ionization enthalpy compared to oxygen.
   • Therefore, Assertion A is correct.
2. Reason R: "The four electrons in 2p orbitals of oxygen experience more electron-electron repulsion."
   • Oxygen's 2p⁴ configuration results in one extra electron pairing up in an already occupied p-orbital, increasing electron-electron repulsion.
   • This repulsion somewhat contributes to easier removal of an electron from oxygen as compared to the symmetrical and stable p-orbitals in nitrogen.
   • Thus, Reason R is correct. However, it describes a contributing factor, not the complete explanation for lower ionization enthalpy.

Conclusion: Both Assertion A and Reason R are correct. However, the primary reason for the higher ionization enthalpy of nitrogen compared to oxygen is the extra stability granted by its half-filled p-orbital. Hence, while Reason R explains a contributing factor, it is not the main reason for the assertion.

The correct answer is: Both A and R are correct but R is NOT the correct explanation of A.