Make correct statements by filling in the symbols $\subset$ or $ \not\subset $ in the blank spaces:

$\{ x:x$ is an equilateral triangle in a plane $\}  \ldots \{ x:x$ is a triangle in the same plane $\} $

Which of the following are sets ? Justify your answer.

The collection of all boys in your class.

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

$\{ 3,4\}  \in A$

In the following state whether $A=B$ or not :

$A=\{a, b, c, d\} ; B=\{d, c, b, a\}$

List all the elements of the following sers :

$B = \{ x:x$ is an integer $; – \frac{1}{2} < n < \frac{9}{2}\} $