Correct answers are:
- Solids can diffuse in liquids. Think of a sugar cube sitting at the bottom of a cup of tea.
- Liquids can diffuse in liquids. Think of a drop of food colouring in water
- It is the process of intermingling atoms from one substance into another.
The other answers are <em>incorrect</em> because:
- Gas molecules are far apart and diffuse rapidly.
- A solid can diffuse into another solid. Pure lead can diffuse into gold, and pure gold can diffuse into lead.
It would be 4.2, hope this helps.