Question

Give one example of the diffusion of a solid in another solid.

Answer 1

If two metal blocks are bound together tightly and kept undistributed for a few years, then the particles of one metal are found to have diffused into the other metal.

For example:

If you write something on the blackboard &leave it uncleaned for a long time you will find difficult to clean the blackboard afterward this is because of the diffusion of chalk particles into the blackboard.