what are 4 common examples in which the size of the reacting particles makes a difference in rate of reaction?

Answer 1

Flour will form an explosive mix in air that wheat or bread crumbs will not.
Steel wool will keep on burning once started that wire or rod steel will not.
Shaved wood will start burning with a match when sawdust (packed) or branches or boards will not.

Answer 2

Here is one off the top of my head, dissolution or dissolving. The lower the surface area of your particles (the larger the size), the more time it will take for them to dissolve.