Please help me with this chemistry question......?

Question

The distance between neighbors of a set of equally spaced atoms in crystalline sodium is 3.72 angstroms. If x-rays with a l=1.579 angstroms are diffracted by this set of parallel planes, calculate the angle 2q at which first-order Bragg reflection is observed.

Answer 1

Well, Bragg Law says: nλ = 2d*sin(q)
Now you give n = 1 (first order), λ = 1.579 A, d = 3.72 A, we can calculate q as:
q = arc sin (nλ/2d) = arc sin (1.579/7.44) = 12.25 (degree)
hence 2q = 24.5 (degree)