Question

Statement I: Oxygen has a smaller first ionization energy than fluorine.
Because
Statement II: Oxygen has a higher $Z_{e}ff$ value than fluorine.

• A. true, false
  
• B. false, true
  
• C. false, false
  
• D. true, true, not correct explanation
• E. true, true, correct explanation

Answer 1

Answer: (A)

Statement I: Oxygen has a smaller first ionization energy than fluorine.
Because in oxygen, after removal of the electron, we get half filled $2p$ orbital which is stable. The first ionization enthalpies of $O$ and $F$ are $1324$ kJ/mol and $1681$ kJ/mol respectively.
Statement II: Oxygen has a lower effective nuclear charge ($Z_{e}ff$) value than does fluorine.
Hence, the statement I is true and the statement II is false.