Which transformation involves flipping a figure across a line?

The transformation that involves flipping a figure across a line is known as a reflection. When a figure is reflected, each point of the original figure is mapped to a corresponding point on the opposite side of a line of reflection, ensuring that the distance from the line to each point remains the same. The line itself acts as a mirror. As a result, the final figure is a mirror image of the original.

In contrast, rotation involves turning a figure around a fixed point, which does not create a flip but rather repositions all points around that center. Translation refers to sliding the figure without altering its orientation or size, and dilations involve resizing the figure while maintaining its shape but not flipping it. Therefore, the correct choice is reflection, which specifically describes the flipping of a figure across a specified line.