What is sets in general collection of things

What is the difference between a collection and a set? Give reasons to support your answer?

What is the difference between a collection and a set? Give reasons to support your answer?

Which of the following are sets? The collection of teachers in a school .

Prove that the number of selections of n things from two sets of n identical things and n other distinct things is (n+2)2^(n-1)

Which of the following are sets? (i) The collection of amazing persons in the world (ii) The collection of all the composite numbers (iii) The collection of all letters of the word INDIAN (iv) The collection of all factors of 32.

Which of the following are sets? (i) The collection of amazing persons in the world (ii) The collection of all the composite numbers (iii) The collection of all letters of the word INDIAN (iv) The collection of all factors of 32.