Which transformation is a flipping of a plane about a fixed line?
a. translation
b. rotation
c. reflection

Reflection

Explanation:

In translation, you just move the whole image to one of the four dimensions (up, down, right or left). The orientation of the shape is kept the same, just the position changes

Rotation of an image usually occurs around a certain point

Reflection , on the other hand, means that the image would be flipped over a given line

Hope this helps :)