Determine whether the following set is finite or infinite:
$\{1, 2, 3, \ldots\}$

In the following,state whether $A = B$ or not:
$A = \{ x: x \text{ is a multiple of } 10 \}$
$B = \{ 10, 15, 20, 25, 30, \ldots \}$

If $A = \{1, 2, 3, 4, 5\}$, then which of the following statements is not true?

If $aN = \{ ax : x \in N \}$,then the set $3N \cap 7N$ is .....$N$.

Which of the following is an example of the null set?
$\{ x : x \in \mathbb{N}, x < 5 \text{ and } x > 7 \}$

If $A = \{1, 2, 3, 4, \dots, 10\}$, then the number of non-empty subsets of $A$ containing only even numbers is