Here's why:

* Rarefaction: A rarefaction is a region of reduced pressure in a medium, like air. In this area, the molecules are spread out, creating lower density.

* Compression: A compression is a region of increased pressure, where the molecules are squeezed closer together, resulting in higher density.

* Reflection: Reflection is the bouncing of waves off a surface. It doesn't directly change the spacing between molecules in a medium.

* Refraction: Refraction is the bending of waves as they pass from one medium to another. While it involves changes in the speed of the waves, it doesn't directly impact the spacing between molecules.

In summary: Rarefactions are characterized by increased space between molecules.