==> \(\lambda = \frac{{xd}}{{nD}} = \frac{{{{10}^{ - 3}} \times 2 \times {{10}^{ - 3}}}}{{n \times 2.5}}\)
\( \Rightarrow \,\,\frac{{8 \times {{10}^{ - 7}}}}{n}m = \frac{{8000}}{n}{ Å }\)
\(n = 1, 2, 3....... \lambda = 8000 Å, 4000 Å, \frac{{8000}}{3}{Å}\,.........\)