The longest wavelength that can be analysed by a sodium chloride crystal of spacing `d = 2.82 Å` in the second order is -

Options

A. `2.82 Å`
B. `5.64 Å`
C. `8.46 Å`
D. `11.28 Å`

Answer

A

Explanation

Bragg’s X-ray diffraction law
`nlamda = 2d sin theta`
`implies lamda = (2d sin theta)/(n)`
For largest `lamda` take `sin theta =1`
Hence, `lamda=(2xx2.82(Å))/(2)=2.82 Å" "["as "n =2 ]`