When will the mutual repulsion of molecules occur?

At distances comparable to the size of the molecules (atoms) themselves, attraction is more noticeable, and with further approach, repulsion. For example, a compressed body is straightened. This is due to the fact that during compression, the molecules are at such a distance from each other when repulsion begins to appear. For example, the compression of a spring, a foam rubber sponge, an eraser to erase a pencil.