State which of the following sets are finite or infinite:
$\{ x : x \in N \text{ and } x \text{ is odd} \}$

Which of the following is an example of the null set?
$\{ y : y \text{ is a point common to any two parallel lines} \}$

Write the following set in the set-builder form: $\{ 2, 4, 8, 16, 32 \}$

Make correct statements by filling in the symbols $\subset$ or $\not\subset$ in the blank spaces:
${ x:x \text{ is an even natural number} } \dots { x:x \text{ is an integer} }$

Let $A = \{1, 2, \{3, 4\}, 5\}$. Which of the following statements is incorrect and why?
${1, 2, 5} \in A$

If ${N_a} = \{an : n \in N\}$,then ${N_5} \cap {N_7} = $