Explanation:
\({\rm{n}}{\mkern 1mu} \,{\rm{\lambda }} = {\rm{2}}{\mkern 1mu} {\rm{d}}\,{\mkern 1mu} {\rm{sin}}\,{\mkern 1mu} {\rm{\theta }}\)
\( \Rightarrow 2 \times 100 = 2 \times {\rm{d}} \times {\rm{sin}}\,{\rm{30}}^\circ \)
\( \Rightarrow 200 = 2 \times {\text{d}} \times 0.5\)\({\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(\because \sin 30^\circ = 0.5)\)
\( \Rightarrow {\text{d}} = \frac{{200}}{{2 \times 0.5}} = 200\,{\text{pm}}\)