According to VBT the extent of overlapping depends upon types of orbitals involved in overlapping and nature of overlapping. More will be the overlapping and the bond energy will also be high.
Which of the following combination of orbitals does not form covalent bond (x-axis is inter nuclear axis) :

Options

A. `s+p_(y)`
B. `p_(y)+p_(y)`
C. `d_(yz)+d_(yz)`
D. `d_(xy)+d_(xy)`

Explanation

To determine which combination of orbitals does not form a covalent bond according to Valence Bond Theory (VBT), we need to analyze the given combinations of orbitals based on their overlapping characteristics.

### Step-by-Step Solution:

1. **Understanding Covalent Bond Formation**:
- Covalent bonds are formed when atomic orbitals overlap. The extent of this overlap determines the bond strength and type of bond formed (sigma, pi, or delta).

2. **Analyzing the First Combination (s and p_y)**:
- The s orbital is spherical and can overlap along the internuclear axis (x-axis).
- The p_y orbital is oriented perpendicular to the x-axis.
- Since the s orbital cannot overlap sidewise with the p_y orbital, this results in **non-bonding overlap**.
- **Conclusion**: This combination does not form a covalent bond.

3. **Analyzing the Second Combination (p_y and p_y)**:
- Both p_y orbitals are oriented along the y-axis.
- They can overlap sidewise, allowing for bonding interactions.
- **Conclusion**: This combination can form a covalent bond.

4. **Analyzing the Third Combination (d_yz and d_yz)**:
- The d_yz orbitals are oriented in the yz-plane.
- They can overlap significantly as they are parallel to each other.
- This results in a strong overlap, potentially forming a delta bond.
- **Conclusion**: This combination can form a covalent bond.

5. **Analyzing the Fourth Combination (d_xy and d_xy)**:
- The d_xy orbitals are oriented in the xy-plane.
- They can also overlap effectively, allowing for bonding interactions.
- This can lead to the formation of a pi bond.
- **Conclusion**: This combination can form a covalent bond.

6. **Final Conclusion**:
- Among the combinations analyzed, the only combination that does not form a covalent bond is the first one: **s and p_y**.

### Answer:
The combination of orbitals that does not form a covalent bond is **s and p_y**.

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