The width is 0.45 cm. The width of the central max is inversely proportional to the slit’s width. The central maximum is known to be the area wherein the light is the most intense and the brightest. Remember n=1, n=450 10x-9m. D=5.0m. To compute for d, you need to do this formula d=1 10x-3m.
You need to multiply the answer that you will get by 2 in order to get the correct answer for central max. If you would follow the formulas mentioned above, you will get letter C as you answer. You can try it out to see if you are going to get the same results.