The transformation rule given is $(x, y) \rightarrow (-x, y)$, which means that the $x$-coordinate changes sign, while the $y$-coordinate remains the same.

This transformation reflects all points across the y-axis, because when reflecting across the y-axis, the $x$-coordinate of any point changes its sign while the $y$-coordinate remains unchanged.

Thus, the correct answer is:

A. A reflection across the y-axis

Would you like more details on how to identify different transformations or have any questions?

Here are 5 related questions to expand on this concept:

1. How would the transformation $(x, y) \rightarrow (x, -y)$ affect a figure on the coordinate plane?
2. What is the result of applying the transformation $(x, y) \rightarrow (-x, -y)$?
3. How does a 90° clockwise rotation about the origin transform the coordinates of a point?
4. Can you describe how a figure would change after a 180° clockwise rotation about the origin?
5. What are the general rules for reflecting a point across both the x-axis and y-axis?

Tip: Always check how transformations affect the $x$- and $y$-coordinates to quickly identify the type of transformation.