Set theory

Which of the followings is a set disjoint from ?

When and , which of the following can be a set ?

If every element of the set is a natural number and satisfy the following condition. When and , which of the following is not necessarily an element of the set ?

Two subsets and of the set are defined as below: , . Find the sum of all elements of the set .

Find the number of subsets of the set that are disjoint from the set .