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COMEDK2024ChemistryClassification of Elements and Periodicity in Properties

Which of the following species has lowest ionisation enthalpy?

Options

  1. AQ
  2. BO ₂
  3. CO ₂⁺
  4. DO ₂⁻

Correct answer

D. O ₂⁻

Step-by-step solution

During addition of electron to O ₂ to form O ₂⁻ , the additional -molecular electron is added to the less stable antibonding orbital. Therefore, it is easier to remove an electron from O ₂⁻ ion to form a neutral O ₂ molecule. Thus ionisation enthalpy of O ₂⁻ is lowest.

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