Assertion :-Among `O_(2)^(+ ) ,O_(2),O_(2)^(-) and O_(2)^(2-)` species, `O_2` is most stable.
Reason :- The bond order of `O_2` is 2.
a. If both Assertion and Reason are CORRECT and Reason is the CORRECT explanation of the Assertion
b. If both Assertion and Reason are CORRECT but Reason is not the CORRECT explanation of the Assertion.
c. If Assertion is CORRECT but Reason is INCORRECT.
d. If Assertion is INCORRECT but Reason is CORRECT.

Options

A. If both Assertion and Reason are CORRECT and Reason is the CORRECT explanation of the Assertion
B. If both Assertion and Reason are CORRECT but Reason is not the CORRECT explanation of the Assertion.
C. If Assertion is CORRECT but Reason is INCORRECT.
D. If Assertion is INCORRECT but Reason is CORRECT.

Answer

To solve the question, we need to analyze the assertion and reason provided, along with the bond orders of the species mentioned.

### Step-by-Step Solution:

1. **Identify the Assertion and Reason**:
- Assertion: Among \( O_2^+, O_2, O_2^-, \) and \( O_2^{2-} \), \( O_2 \) is the most stable.
- Reason: The bond order of \( O_2 \) is 2.

2. **Calculate the Bond Order of Each Species**:
- **For \( O_2^+ \)**:
- Total electrons: 15
- Bonding electrons: 10 (from \( \sigma \) and \( \pi \) orbitals)
- Antibonding electrons: 5
- Bond order = \( \frac{10 - 5}{2} = 2.5 \)

- **For \( O_2 \)**:
- Total electrons: 16
- Bonding electrons: 10
- Antibonding electrons: 6
- Bond order = \( \frac{10 - 6}{2} = 2 \)

- **For \( O_2^- \)**:
- Total electrons: 17
- Bonding electrons: 10
- Antibonding electrons: 7
- Bond order = \( \frac{10 - 7}{2} = 1.5 \)

- **For \( O_2^{2-} \)**:
- Total electrons: 18
- Bonding electrons: 10
- Antibonding electrons: 8
- Bond order = \( \frac{10 - 8}{2} = 1 \)

3. **Stability Order Based on Bond Order**:
- The stability order based on bond order is:
- \( O_2^+ \) (2.5) > \( O_2 \) (2) > \( O_2^- \) (1.5) > \( O_2^{2-} \) (1)
- Therefore, \( O_2^+ \) is the most stable species, not \( O_2 \).

4. **Evaluate the Assertion**:
- The assertion is incorrect because \( O_2^+ \) is the most stable, not \( O_2 \).

5. **Evaluate the Reason**:
- The reason states that the bond order of \( O_2 \) is 2, which is correct.

6. **Conclusion**:
- Assertion is INCORRECT.
- Reason is CORRECT.

### Final Answer:
**d. If Assertion is INCORRECT but Reason is CORRECT.**