Here are the answers to the questions: 1. a, b, d are correct. Grain boundary character cannot be measured using XRD. 2. d is incorrect. Crystallite sizes below 1000 Å have errors greater than 20% when using Scherrer equation to calculate size from XRD peak broadening. 3. FCC structure: 1) 2θ = 44.7°, (111) 2) 2θ = 51.8°, (200) 3) 2θ = 75.5°, (220) 4. Use Scherrer equation: B = Kλ / t cosθ For 10°: t = 880 Å For 45°