From Eq$.15\mathrm{.}11$ it can be seen that for a fixed l $,$ the interplanar

spacing $($ d hkl$>$n $)$ is inversely proportional to sin u $.$ In other

words, scattering corresponding to the smallest$$ spacing

occurs at the maximum value of sin u $($when u $=90).$ If

l $=0\mathrm{.}154$ nm X$-$rays are used, what is the theoretical

limit of resolution? $($That is$,$ what is the minimum spacing

observable?$)$