Which of the following collections are sets?
(i) The collection of honest persons in india
(ii) The collection of all prime number between 14 and 50.
(iii) The collection of all factor of 24 which are less than 20.
(iv) The collection of all the rivers of india.

Explanation

(i) The concept of honest person is not well defined as there is no such rule for decideing whether a particular person is honest or not.
`therefore` Given collection is not a set.
(ii) A natural number 'p' is called a prime number if it has exactly two factors 1 and p (itself). Prime =number between 14 and 50 are 17,19,23,29,31,37,41,43,47.
`therefore` Given collection is a set and contains 17,19,23,29,31,37,41,43,47.
(iii) The factor of 24 are 1,2,3,4,6,8,12,24
and out of these 1,2,3,4,6,8,12 are less than 20.
`therefore` Given collection is a set and contains 1,2,3,4,8,12.
(iv) Rivers in india are Ganga, Yamuna, Indus, Bramhmputra, Tapi, Narmada, Godavari, Krishna, Mahanadi and kaveri etc.
`therefore` Given collection is a set and contains above mentioned rivers.