X-Ray Diffraction Question

[rocksalt]

I know it is a simple question but I cannot find the answer. Why is the [001] diffraction peak not observed in XRD but [004] peak is observed. Thank you.

 

[Gokul43201]

Your statement is not generally true (though it is true for simple crystal systems like the BCC, FCC, diamond cubic, etc). But in any case, you need to look up the section on Structure Factor in your XRD textbook.