To determine which statement is incorrect according to molecular orbital theory, we need to analyze the provided statements regarding the molecular orbitals of the C2 molecule and its anion C2²⁻.
### Step-by-Step Solution:
1. **Understanding the C2 Molecule:**
- The C2 molecule has a total of 12 electrons (6 from each carbon atom).
- The molecular orbital configuration for C2 is:
- σ1s², σ1s*², σ2s², σ2s*², (π2p_y)², (π2p_z)², σ2p_x²
- The LUMO (Lowest Unoccupied Molecular Orbital) for C2 is σ2p_x, which is the next orbital after all the filled ones.
2. **Analyzing the Statements:**
- **Statement 1:** "LUMO level for C2 molecule is σ2p_x orbital."
- This statement is **correct** because σ2p_x is indeed the LUMO for C2.
- **Statement 2:** "In C2 molecules, both bonds are π bonds."
- This statement is **incorrect**. C2 has a total of two π bonds and one σ bond. The σ bond is formed by the overlap of the 2p orbitals along the internuclear axis, while the π bonds are formed by the side-to-side overlap of the remaining 2p orbitals.
- **Statement 3:** "In C2²⁻, there is one σ bond and two π bonds."
- This statement is **correct**. C2²⁻ has a total of 14 electrons, and the molecular orbital configuration is:
- σ1s², σ1s*², σ2s², σ2s*², (π2p_y)², (π2p_z)², σ2p_x²
- This configuration indicates there are indeed two π bonds and one σ bond.
- **Statement 4:** "C2 is paramagnetic but C2²⁻ is diamagnetic."
- This statement is **incorrect**. C2 has unpaired electrons, making it paramagnetic, while C2²⁻ has all paired electrons, making it diamagnetic.
3. **Conclusion:**
- The incorrect statements are:
- "In C2 molecules, both bonds are π bonds." (Statement 2)
- "C2 is paramagnetic but C2²⁻ is diamagnetic." (Statement 4)
### Final Answer:
The incorrect statement according to molecular orbital theory is: "In C2 molecules, both bonds are π bonds."
