Answer;
-A wave with the longest wavelength.
Explanation;
-Diffraction is the apparent of wave through,around small obstacles and the spreading out of wave past small openings. When thinking of diffraction of a wave think of shining a flashlight around a corner. The light bends around the corner but there is a place where it is dark and the light does not hit. Diffraction of a wave is basically the wave bending around an object then dispersing out.
-The amount of diffraction (the sharpness of the bending) increases with increasing wavelength and decreases with decreasing wavelength. When the wavelength of the waves is smaller than the obstacle, no noticeable diffraction occurs.