The element that has a Kα line in its X-ray spectrum with a wavelength of 1,785 Å is Copper (Cu). The Kα line is a characteristic X-ray emission line that results from electron transitions within the innermost electron shell (K-shell) of an atom. Copper has a strong Kα line with a wavelength of approximately 1,785 Å (angstroms). This particular X-ray emission is often used as a reference line in X-ray spectroscopy and diffraction experiments.