What phenomena indicate that molecules are repelled from each other?

If there would be no mutual repulsion, then all substances had the same density. For example, tearing a piece of paper apart would be as difficult as bending an iron beam with your hands. Moreover, no human or machine could separate the molecules.
Diffusion. If there was no mutual repulsion, then we would not be able to smell. Moreover, we would not be able to smell at all.
Brownian motion. Brownian motion is the most obvious and striking example of the repulsion of molecules.