Finite and infinite set:
A set is finite if you can list all its elements and infinite otherwise.
All sets described above are finite because you can list or count all their elements
However, among the five sets, one set can be turned into an infinite set with one small change. That set is set number 3
If I get rid of the word positive and say instead "the set of all numbers less than 10" the set in now infinite because you cannot count all those numbers less than 10.