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. `11.28Å`

Answer

A

Explanation

`2d sin phi = n lambda`
`n = (2d)/(lambda) sin phi, n = 2`
`lambda = (2d)/(2) sin phi`
for `lambda_(max), sin phi = 1`
`lambda = (2d)/(2) = d = 2.8 Å`