Question

Which of the following does not describes a dilation?

Answer 1

An Isometry does not describe a dilation. To dilate an image would be to change the size of an image, specifically by a certain amount, which is called the scale factor.

An expansion and retraction both change the size of the image, meaning that they do apply to dilation. An image is always expanded or retracted by a scale factor.
 
For example, if I were to double the size of an image, I would be dilating it by a scale factor of 2. If I were to retract an image to half of it's original size, I would be dilating the image by a scale factor of 1/2. 

An Isometry is defined by a transformation that is invariant with respect to distance. This only means that the size and shape of the image will not change. Examples of isometries are translations, reflections, and rotations. 

Therefore, with the given information, the answer must be Isometry.