The graph shows the variation of fringe width $(X)$ versus the distance of the screen from the plane of the slits $(D)$ in Young's double-slit experiment (keeping other parameters constant,where $d$ is the distance between the slits). The wavelength of light used can be calculated as:

• A
  slope $\times d^2$
• B
  $\frac{d}{\text{slope}}$
• C
  $\frac{\text{slope}}{d}$
• D
  slope $\times d$