Collection of all integers is well defined as we know about all the integers that are odd

i.e., {1,3,5,7,9,.....,-1,-3,-5,-7,....}

Hence, the collection forms a set.

The collection of eleven best cricket batsmen in the world is finite and well defined and is therefore a set. 

Collection of natural numbers between 100 and 200 (both inclusive) is well defined as we know about all the natural numbers that fall between the two numbers i.e., {100, 101, 102,...., 199, 200}.

Hence, the collection forms a set.

The collection of all months of the year beginning with J = {January, June, July}

The collection is well defined and hence it forms a set.

Collection of ten most talented writers of India is a finite  different examples in this chapter is well defined as we know all the different examples in this chapter.

Hence, the collection forms a set.