When radio waves encounter a mountain, they may bend around it, demonstrating which property of waves?

Answer 1

diffraction

Answer 2

I don't know the word you are seeking but there are two ways that radio waves can reach the far side of a mountain.
1. The wave length of the radio wave is large compared to the object(the mountain) that is in the way.
2. The wave reflects off the ionosphere. The ionosphere is a layer of the atmosphere that has lots of charged particles present and reflects some radio signals when the angle of incidence is shallow enough.