Solution:

(i) A group of eleven of the world’s best cricket batsmen is not a well-defined collection.

Because the criteria used to determine a batsman’s talent differ from person to person.

As a result, this collection does not form a set.

(ii) The collection of all boys in your class can be considered as well-defined collection.

Because a boy who belongs to this collection can be identified .

As a result, this collection can be considered a set.