Which of the following statements is not correct regarding bonding molecular orbital ?

Options

A. Bonding molecular orbitals possess less energy than the atomic orbitals from which they are formed.
B. Bonding molecular orbitals have low electron density between the two nucleus
C. Every electron in bonding molecular orbitals contributes to the attraction between atoms
D. They are formed when the lobes of the combining atomic orbitals have same sign

Answer

To determine which statement is not correct regarding bonding molecular orbitals, let's analyze each statement step by step.

### Step 1: Analyze Statement A
**Statement A:** Bonding molecular orbitals possess less energy than the atomic orbitals from which they are formed.

- **Explanation:** This statement is correct. Bonding molecular orbitals are formed when atomic orbitals combine constructively, resulting in a lower energy state compared to the original atomic orbitals. Thus, they are more stable.

### Step 2: Analyze Statement B
**Statement B:** Bonding molecular orbitals have low electron density between the two nuclei.

- **Explanation:** This statement is incorrect. Bonding molecular orbitals actually have high electron density between the two nuclei. This high electron density is what leads to the attractive forces that hold the atoms together in a molecule. Therefore, this statement is the one that is not correct.

### Step 3: Analyze Statement C
**Statement C:** Every electron in the bonding molecular orbitals contributes to the attraction between atoms.

- **Explanation:** This statement is correct. Electrons in bonding molecular orbitals do contribute to the attractive forces between the nuclei of the atoms involved in the bond. Each pair of electrons in a bonding orbital helps to stabilize the bond.

### Step 4: Analyze Statement D
**Statement D:** They are formed when the lobes of combining atomic orbitals have the same sign.

- **Explanation:** This statement is also correct. Bonding molecular orbitals are formed when the lobes of the combining atomic orbitals have the same sign (constructive interference). This leads to an increase in electron density between the nuclei.

### Conclusion
Based on the analysis, the statement that is not correct regarding bonding molecular orbitals is **Statement B**.

### Summary of the Solution
- **Correct Statements:** A, C, D
- **Incorrect Statement:** B