If ${N_a} = \{an : n \in N\}$,then ${N_3} \cap {N_4} = $

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

Consider the sets $\phi, A=\{1,3\}, B=\{1,5,9\}, C=\{1,3,5,7,9\}$. Insert the symbol $\subset$ or $\not\subset$ between the pair of sets: $A, \ldots B$.

List all the elements of the following set:
$C = \{ x : x \text{ is an integer; } x^2 \le 4 \}$

If $Q = \{x : x = \frac{1}{y}, y \in N\}$,then which of the following is true?

Make correct statements by filling in the symbols $\subset$ or $\not\subset$ in the blank spaces:
${ x:x \text{ is a circle in the plane} } \dots { x:x \text{ is a circle in the same plane with radius } 1 \text{ unit} }$