Difficult to program using Scratch (but not impossible). But fun to act out and to reinforce the idea of how an algorithm helps solve problems.
Imagine you’ve got items that need sorting. They are in a random order. How can you sort them out and know that every item is in the right place? As a human, it’s intuitive. You can see that people are in the right height order or age order. You just sort them without thinking. Well, you are thinking but you “just know” how to do it.
How would a computer do it?
One way is the BUBBLE sorting algorithm.