The metal niobium has a BCC crystal structure. If the angle of diffraction

The metal niobium has a BCC crystal structure. If the angle of diffraction for the (211) set of planes occurs at 75.99? (first-order reflection) when monochromatic x-radiation having a wavelength of 0.1659 nm is used, compute (a) the interplanar spacing for this set of planes, and (b) the atomic radius for the niobium atom.