Predict correct statement.

Options

A. E_(ea) gt 0 (E_(ea) = Electron affinity) implies that electron attachment is exothermic
B. Electron gain enthalpy of O^- ion is negative
C. The electron gain enthalpy of a species X is the negative of the ionization enthalpy is of its negative ion
D. Both (1) & (3)

Answer

To solve the question regarding the correct statements about electron affinity and electron gain enthalpy, let's break it down step by step:

### Step 1: Understanding Electron Affinity
- **Definition**: Electron affinity (EA) is the amount of energy released when an electron is added to a neutral atom in the gas phase. A higher electron affinity indicates a greater tendency to gain an electron.
- **Comparison of Oxygen and Sulfur**:
- Oxygen (O) is in the second period, while Sulfur (S) is in the third period of the periodic table.
- Due to the larger atomic size of sulfur, it can accommodate an additional electron more easily than oxygen. Therefore, the electron affinity of sulfur is greater than that of oxygen.

### Step 2: Evaluating the First Statement
- The first statement claims that sulfur's electron affinity is greater than that of oxygen.
- **Conclusion**: This statement is **true** because sulfur can accommodate an electron more easily due to its larger size and lesser electron-electron repulsion compared to oxygen.

### Step 3: Understanding Electron Gain Enthalpy
- **Definition**: Electron gain enthalpy is the change in enthalpy when an electron is added to a neutral atom, typically expressed as a negative value for exothermic processes.
- **Oxygen's Electron Gain Enthalpy**: When oxygen gains an electron to form O⁻, this process is exothermic (releases energy). However, adding another electron to O⁻ to form O²⁻ is endothermic (requires energy) due to increased electron-electron repulsion.

### Step 4: Evaluating the Second Statement
- The second statement claims that the electron gain enthalpy of O⁻ is negative.
- **Conclusion**: This statement is **false** because the process of adding an electron to O⁻ (to form O²⁻) is endothermic, meaning the electron gain enthalpy would be positive, not negative.

### Step 5: Understanding the Relationship Between Ionization Enthalpy and Electron Gain Enthalpy
- **Definition**: Ionization enthalpy is the energy required to remove an electron from a neutral atom. The electron gain enthalpy is the reverse process.
- The relationship states that the electron gain enthalpy of a species (X) is the negative of the ionization enthalpy of its negative ion (X⁻).

### Step 6: Evaluating the Third Statement
- The third statement claims that the electron gain enthalpy of species X is the negative of the ionization enthalpy of its negative ion.
- **Conclusion**: This statement is **true** because it accurately describes the relationship between the two processes.

### Final Conclusion
- **Correct Statements**: The first and third statements are correct, while the second statement is incorrect. Therefore, the correct answer is option D (both first and third are correct).