What are the types of Infinite subsets as subset of real number - in closed open and semi open interval

What are the types of Subsets of real number?

what is Subset of A

What are the elements of a subset?

Set of natural numbers is a subset of

What are closed pipe and open pipe ?

Mark the following subsets of set R of real numbers on the number line and write them intervals: {x:x in R, x ge 3}

What are the subsets of {O/,{O/}} .

Continuity in open interval and closed interval