Item 2.

Here we are looking for the set of all \(x^2\)s where \(x\) is a natural number. So this set is simply the set of perfect squares. \(B = \{0, 1, 4, 9, 16, \ldots\}\text{.}\)

Another way we could have written this set, using more strict set builder notation, would be as \(B = \{x \in \N \st x = n^2 \text{ for some } n \in \N\}\text{.}\)