White light is used to illuminate the two slits in a Young's
double slit experiment. The separation between the slits is b and the screen is at
a distance `d(gtgtb)` from the slits. At a point on the screen directly in front of
one of the slits, certain wavelengths are missing. Some of these missing
wavelength are
`(a) lambda = b^2//d (b) lambda=2b^2//d (c) lambda = b^2//3d (d)lambda = 2b^2//3d ` .