Assertion : `O_(2)` molecule is diamagnetic while `C_(2)` molecule is paramagnetic in nature.
Reason : Bond order of `O_(2) ` molecule is `1.5` and that of `C_(2)` molecule is `2.5` .

Options

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

Explanation

To analyze the given assertion and reason, we will break down the information step by step.

### Step 1: Understand the Assertion
The assertion states that the O₂ molecule is diamagnetic while the C₂ molecule is paramagnetic.

- **Diamagnetic** substances are those that do not have unpaired electrons and are not attracted to a magnetic field.
- **Paramagnetic** substances have unpaired electrons and are attracted to a magnetic field.

### Step 2: Analyze the O₂ Molecule
- The electronic configuration of O₂ can be represented as:
\[ \text{O}_2: (1\sigma)^2 (1\sigma^*)^2 (2\sigma)^2 (2\sigma^*)^2 (2\pi)^2 (2\pi^*)^1 (2\pi^*)^1 \]
- In this configuration, O₂ has 2 unpaired electrons in the antibonding π orbitals (2π*). Therefore, O₂ is **paramagnetic**, not diamagnetic.

### Step 3: Analyze the C₂ Molecule
- The electronic configuration of C₂ can be represented as:
\[ \text{C}_2: (1\sigma)^2 (1\sigma^*)^2 (2\sigma)^2 (2\pi)^2 \]
- In this configuration, C₂ has no unpaired electrons. Therefore, C₂ is **diamagnetic**, not paramagnetic.

### Step 4: Understand the Reason
The reason states that the bond order of O₂ is 1.5 and that of C₂ is 2.5.

- The bond order is calculated using the formula:
\[ \text{Bond Order} = \frac{(\text{Number of bonding electrons} - \text{Number of antibonding electrons})}{2} \]
- For O₂:
- Bonding electrons = 10 (from σ and π orbitals)
- Antibonding electrons = 6 (from σ* and π* orbitals)
- Bond Order = (10 - 6) / 2 = 2
- For C₂:
- Bonding electrons = 8
- Antibonding electrons = 0
- Bond Order = (8 - 0) / 2 = 4

### Conclusion
- The assertion that O₂ is diamagnetic is **false**; it is paramagnetic.
- The reason that the bond order of O₂ is 1.5 and that of C₂ is 2.5 is also **false**; the correct bond orders are 2 for O₂ and 2 for C₂.

### Final Answer
Both the assertion and reason are false.