Which of the following state of matter has the highest rate of diffusion?

The intermolecular attraction in the case of solids is more so they have less space between particles. The intermolecular attraction in the case of liquids is less than in solids and the space between particles is more. That's why the rate of diffusion in liquids is higher than in solids. And it is maximum for gases because the gaseous particles have the least intermolecular forces of attraction in between them.