Select correct statement(s) regarding `sigma and pi` bonds :

Options

A. `sigma` - bond lies on the line joining the nuclei of bonded atoms
B. `pi` - electron cloud lies on either side to the line joining the nuclei of bonded atoms
C. `(2p_(pi)-3d_(pi)) pi` - bond is stronger than `(2p_(pi)-3p_(pi))pi` - bond.
D. `sigma`-bond has primary effect to decide direction of covalent bond, while `pi`- bond has no primary effect in direction of bond

Answer

To address the question regarding the correct statements about sigma and pi bonds, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Sigma Bonds**:
- **Statement A**: "Sigma bond lies on the line joining the nuclei of bonded atoms."
- **Explanation**: Sigma bonds are formed by the head-on (axial) overlap of atomic orbitals. This overlap occurs along the line connecting the two atomic nuclei. Therefore, this statement is **correct**.

2. **Understanding Pi Bonds**:
- **Statement B**: "Pi electron cloud lies on either side of the line joining the nuclei of the bonded atoms."
- **Explanation**: Pi bonds are formed by the sideways overlap of p orbitals. The electron density in a pi bond is found above and below the plane of the nuclei of the bonded atoms, which aligns with this statement. Thus, this statement is also **correct**.

3. **Comparing Bond Strength**:
- **Statement C**: "2pπ - 3dπ bond is stronger than 2pπ - 3pπ."
- **Explanation**: The strength of bonds generally increases with the extent of orbital overlap. The d orbitals are more directional compared to p orbitals, which allows for stronger interactions when forming bonds. Therefore, the 2pπ - 3dπ bond is indeed stronger than the 2pπ - 3pπ bond, making this statement **correct**.

4. **Role of Sigma and Pi Bonds in Molecular Geometry**:
- **Statement D**: "Sigma bond has a primary effect to decide the direction of covalent bond while pi bond has no primary effect in the direction of bond."
- **Explanation**: In molecular geometry, the arrangement of sigma bonds determines the overall shape of the molecule, while pi bonds do not affect the geometry significantly. Therefore, this statement is also **correct**.

### Conclusion:
All statements A, B, C, and D regarding sigma and pi bonds are correct.