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Hint
$I(0)$ is proportional to $\Delta\mathrm{SLD}^2 V^2$, where $\Delta\mathrm{SLD} = \mathrm{SLD}_\mathrm{particle} - \mathrm{SLD}_\mathrm{solvent}$ is the contrast (or, excess scattering length density) and $V$ is the particle volume.
$I(0)$ is proportional to $\Delta\mathrm{SLD}^2 V^2$, where $\Delta\mathrm{SLD} = \mathrm{SLD}_\mathrm{particle} - \mathrm{SLD}_\mathrm{solvent}$ is the contrast (or, excess scattering length density) and $V$ is the particle volume.