In an experiment to identify an unknown spectral line, monochromatic light passes through a single slit that is 0.10 mm wide and forms a diffraction pattern on a screen 2.0 m away. The first dark band is observed 2.5 cm above the central bright region on the screen.
(1) Determine the diffraction angle that corresponds to the first minimum.
(2) Calculate the wavelength of the unknown light. Express your answer in nanometres.
(3) State whether the calculated wavelength falls within the visible spectrum and justify your answer.