Given below are two statements: Statement I: Fluorine has the most negative electron gain enthalpy in its group. Statement II: Oxygen has the least negative electron gain enthalpy in its group. In the light of the above statements, choose the most appropriate option from the options given below:
Both Statement I and Statement II are true
Statement I is true but Statement II is false
Both Statement I and Statement II are false
Statement I is false but Statement II is true
Correct answer:D
Standard Method
Given: Two statements about electron gain enthalpy in Group 17 and Group 16.
Find: Which option correctly identifies the truth value of Statement I and Statement II.
Electron gain enthalpy becomes more negative across a period, but exceptions occur within groups due to very small atomic size and increased electron-electron repulsion.
For Statement I, fluorine does not have the most negative electron gain enthalpy in its group. In Group 17, chlorine has a more negative electron gain enthalpy than fluorine because the incoming electron experiences greater repulsion in the very compact fluorine atom. Therefore, Statement I is false.
For Statement II, oxygen has the least negative electron gain enthalpy in Group 16. Its small size causes greater electron-electron repulsion when an extra electron is added. Therefore, Statement II is true.
Hence, the correct conclusion is: Statement I is false but Statement II is true.
The correct option is D.
Detailed Explanation
Given:
Find: The most appropriate option.
Analysis of Statement I: Electron gain enthalpy is the energy change when an electron is added to an isolated gaseous atom. Although electron gain enthalpy generally becomes more negative across a period, fluorine is an exception within its group. In the halogen group, chlorine has more negative electron gain enthalpy than fluorine. The reason is the very small size of fluorine, which leads to strong electron-electron repulsion in its compact valence shell when an extra electron is added.
So, Statement I is false.
Analysis of Statement II: Oxygen belongs to Group 16. Oxygen has the least negative electron gain enthalpy in its group because its compact size causes greater repulsion when the added electron enters the atom.
So, Statement II is true.
Conclusion: The correct statement is Statement I is false but Statement II is true.
Therefore, the correct option is D.
Assuming electron gain enthalpy always becomes more negative up a group is incorrect. Small atoms like fluorine and oxygen show exceptions because added electrons face greater electron-electron repulsion. Always check known anomalies before applying the trend.
Confusing fluorine with chlorine in Group 17 is a common mistake. Chlorine has the more negative electron gain enthalpy, not fluorine. Compare atomic size and repulsion effects instead of using only electronegativity intuition.
Treating oxygen like a perfectly regular group member is wrong. Oxygen has the least negative electron gain enthalpy in Group 16 due to its very small size. Remember that compact orbitals can reduce the favorability of adding an electron.
Get unlimited AI-adaptive practice, mastery tracking, and an AI tutor that explains every step — free to start.
