Answer:
Option. B is not describing the a rigid transformation.
Explanation:
Rigid transformation means an object when moved from one point to another, its position may change but size and shape of the object remains unchanged.
By this definition,
Option A. translating a figure 4 units up
In this statement only place is moving not the size, so it's Correct (describing rigid transformation)
Option B. Enlarging a figure by a scale factor of 2.
In this option size of the object is enlarged by a scale scale factor of 2, so this option is Not correct (not describing rigid transformation)
Option C. Rotating a figure by 180°
Again place is changing so its describing the rigid transformation. Correct (describing rigid transformation).
Option D. Reflecting a figure across the y axis.
Reflection means change in place. So the option is Correct (describing rigid transformation).