Effective overlapping will be shown by:

Options

A.
B.
C.
D. All the above

Explanation

To determine which option shows effective overlapping, we need to analyze the types of overlapping presented in the options A, B, C, and D.

### Step-by-Step Solution:

1. **Understanding Overlapping Types**:
- Overlapping can be categorized into two main types: head-on (or end-to-end) overlapping and side-wise (or lateral) overlapping.
- Head-on overlapping generally leads to stronger bonds compared to side-wise overlapping.

2. **Analyzing Option A**:
- Option A describes head-on overlapping of two p-orbitals, but it is noted that the overlapping is negative due to opposite signs (one p-orbital is positive and the other is negative).
- Since the overlapping is negative, this type of overlap is not effective.

3. **Analyzing Option B**:
- Option B describes side-wise overlapping of two p-orbitals.
- Here, the overlapping is also negative (one p-orbital is positive and the other is negative).
- Side-wise overlapping is less effective than head-on overlapping, and since this is also negative, it is not effective.

4. **Analyzing Option C**:
- Option C describes head-on overlapping of two p-orbitals where both lobes have the same sign (both positive or both negative).
- This results in positive overlapping, which is effective and leads to stronger bonding.

5. **Analyzing Option D**:
- Option D states "all of the above." However, since options A and B are not effective, D cannot be correct.

6. **Conclusion**:
- The option that shows effective overlapping is **C**, which involves head-on overlapping with positive overlap.

### Final Answer:
The effective overlapping will be shown by option **C**.