In Young's double slit experiment, carried out with light of wavelength A = 5000 A0 tif the distance between the third minima on the either side of the central maxima is 25mm  and the screen is at 200 cm from the slits. then the distance between the slits is

in Young's double slit  experiment if the fringe width is β then the distance between the  first two minima on the either side of the central maxima is β then separation between the second minima on the either side of the central maxima is 3 β  and between third minima on either side is 5βSo 5β =25 mm  β = 5mmλDd=5×10-3d=λD5×103=5×10-7×25×103=2×10-4