Geometry

Question Analysis:
This question tests whether you understand the property of reflection across the line , specifically for points that lie on the line itself.  
The main focus is on the behavior of points that are located on the line of reflection.

Key Concept Explanation:
- Reflection across the line : When reflecting a point across the line , the coordinates are swapped.
However, any point that already lies on the line will remain unchanged because its coordinates are equal to each other — the point is already its own reflection.
- For example, if the point is , reflecting it across results in again because both coordinates are identical.

Step-by-Step Solution:
- A point lies on the line if .  
- When reflecting this point across the line