Final answer:
Dilation is the transformation that does not preserve congruence since it changes the size of the figure, whereas rotation, reflection, and translation maintain the size and shape of figures, thus preserving congruence.
Step-by-step explanation:
The transformation that does not preserve congruence is (b) Dilation.
A rotation is a type of transformation that turns a figure about a fixed point called the center of rotation. A reflection flips a figure over a line, known as the line of reflection. A translation slides a figure from one position to another without turning or flipping it. Each of these transformations preserves the size and shape of figures, hence maintaining congruence. However, a dilation rescales a figure by a given factor, which changes the size of the figure, therefore it does not preserve congruence. Congruence implies that figures have the same size and shape, which is not the case after a dilation unless the dilation factor is one.