Which of the following collections is not a set?
Names of 10 most renowned actors
A set is a well-defined collection of objects.
Option A → vowels in English alphabet are a, e, i, o, u. So, this is a set.
Option B → All natural numbers that divide 42 are 1, 2, 3, 6, 7, 14, 21, 42. This is also a set.
Option C → This collection is not well-defined, because the criterion for selecting an actor as most renowned may vary from a person to other. So, option C does not represent a set.
Option D → Though we may not immediately recollect all the river names, the collection is well-defined
i.e., given a river name, we can say whether it belongs to this set (or) not.