In a Young's double slit experiment the slit is illuminated by a source having two wavelengths of 400 nm and 600 nm. If distance between slits, d=1 mm , and distance between the plane of the slit and screen, D=10 m then the smallest distance from the central maximum where there is complete darkness is:
(a) 2 mm
(b) 3 mm
(c) 12 mm
(d) there is no such point