Which object would produce the most distinct diffraction pattern, an apple, a pencil lead, a human h

human hair because of it is very thin and would produce the same effect as the slits in a board.

Which object would produce the most distinct diffraction pattern, an apple, a pencil lead, a human hair. why ?

Diffraction pattern in what kind of wave? The best diffraction patterns are produced by barriers slightly larger than the wavelength of the wave.

Light waves? Try your hair.

Water waves in the bathtub? Try the apple.