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. `2.82overset(@)A`
B. `5.64overset(@)A`
C. `8.46overset(@)A`
D. `11.28overset(@)A`

Answer

A

Explanation

Use Bragg's X-ray diffraction law,
`" " nlambda=2d sin theta`
` :. " " lambda=(2d sin theta)/(n)`
For longest atomic wavelength `sin theta =1`
`:. " " lambda=(2xx2.82(Å))/(2)" " [ :. N=2` for second order]
`" " =2.82 Å`