6. (5%) A single crystal of table salt (NaCl) is irradiated with a beam of X rays of wavelength 0.250 nm, and the first Bragg reflection is observed at an angle of 300. What is the atomic spacing of NaCl?
(A) 0.250
(B) 0.5
(C) 0.125 nm
(D) 0.250 nm
(E) 0.500 mm. 

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