Assertion: Formation of `Cl^(-)` ion is exothermic wheres `O^(2-)` ion formation is endothermic.
Reason: `EA_(2)` of oxygen is endothermic and greater than its exothermic `EA_(1)` value of oxygen.

Options

A. If both assertion and reason are true annd the reason is the correct explanation of assertion
B. If both assertion and reason are true but reason is not the correct explanation of assertion
C. If assertion is true but the reason is false
D. if assertion is false but the reason is true

Answer

To solve the question, we need to analyze the assertion and reason statements regarding the formation of the `Cl^(-)` and `O^(2-)` ions.

### Step 1: Understand the Assertion
The assertion states that the formation of the `Cl^(-)` ion is exothermic, while the formation of the `O^(2-)` ion is endothermic.

- **Formation of `Cl^(-)` ion**: Chlorine (Cl) has an atomic number of 17 and has 7 valence electrons. To achieve a stable noble gas configuration (similar to Argon), it needs to gain one electron. The process of gaining an electron releases energy, making it exothermic.

### Step 2: Understand the Reason
The reason states that the second electron affinity (`EA_(2)`) of oxygen is endothermic and greater than its first electron affinity (`EA_(1)`) value, which is exothermic.

- **Formation of `O^(2-)` ion**: Oxygen (O) has an atomic number of 8 and has 6 valence electrons. It can gain one electron to form `O^(-)` (exothermic process). However, to gain a second electron and form `O^(2-)`, the process becomes endothermic. This is because the added electron experiences repulsion from the already present electrons in the valence shell, requiring energy input.

### Step 3: Conclusion
Both the assertion and reason are correct:
- The formation of `Cl^(-)` is indeed exothermic.
- The formation of `O^(2-)` is endothermic due to the reasons stated.

### Final Answer
Both the assertion and reason are true, and the reason correctly explains the assertion.