Answer:
1. A solid can diffuse into a liquid, but a solid cannot diffuse into another solid.
3. A liquid can diffuse into another liquid.
4. A gas can diffuse into another gas.
Explanation:
When an object is in liquid or gas form, they can easily move and spread. This is because the molecules are packed loosely. Since they can move freely, diffusion on and into gas/liquid can be easily achieved.
Solid form can diffuse into liquid too. Seawater is mostly made of water and solid salt. But diffusing a solid into a solid is not possible since the molecule is tightly packed and barely moves. The diffusion might be happening, but at a really slow rate that we can assume it is not.