Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:

$ 4\, ......... \, A $

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

$\{ 3,4\}  \subset A$

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

$\{1,2,5\}\in A$

Examine whether the following statements are true or false :

$\{ a,e\}  \subset \{ x:x$ is a vowelin the English alphabet $\} $

Given the sets $A=\{1,3,5\}, B=\{2,4,6\}$ and $C=\{0,2,4,6,8\},$ which of the following may be considered as universal set $(s)$ for all the three sets $A$, $B$ and $C$

$\{ 1,2,3,4,5,6,7,8\} $

Which of the following are examples of the null set

Set of odd natural numbers divisible by $2$