Look at the black, two way arrow in the image showing the distance between two nearest wave troughs. The distance between 3 angstroms and 2 angstroms is 1 angstrom. That means the length of this wave is 1 angstrom. What type of light has a wavelength of 1 angstrom?
If you don't know now, don't worry! You'll know the answer by the end of this light tour!