In young's double slit experiment the distance between the sources is 7.7 μm . If the wavelength of light used is 500 nanometre, the angular position of the six dark fringe from the  centre fringe is

Distance between the slits d=7.7 μm=7.7×10−6 m Wavelength λ=500 nm=500×10−9 m Number of fringes n=6 Angular position θ=(2n−1)λ2d                              =  (2×6−1) ×500  × 10−92  × 77 × 10−7                                  = 11×52×777                                  =0.357 rad