(a) An X-ray diffractometer recorded diffraction peaks of an element at following 2 values in degrees: 38.7,45.1,65.6,78.8,83.0 and 99.6. If the wavelength of the X-rays was 1.54A, determine (i) The crystal structure of the element (ii) The Miller indices of diffracting planes. (iii) The lattice constant of element. (b) Briefly (in less than 40 words) explain why? (i) Grain boundaries remain in high-energy state than the grains. (ii) If the critical radius ratio for triangular coordination around a central cation in an ionic crystal is less than 0.155, the system becomes unstable. (iii) (100) reflection is absent in XRD pattern of FCC crystals