Question

What is the relation between intermolecular spaces and diffusion

Answer 1

Intermolecular literally means between molecules. Intermolecular space is the distance between molecules.
For example the intermolecular spaces for liquid substances is much less than the intermolecular spaces for substances in the gas phase.
Diffusion is the net movement of molecules or atoms from a region of high concentration (or high chemical potential) to a region of low concentration (or low chemical potential) as a result of random motion of the molecules or atoms.
When intermolecular space increases, diffusion also increases.
For gas, have higher diffusion rate than liquid and gas.