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

$\{ x:x$ is a student of class $\mathrm{XI}$ of your school $\}  \ldots \{ x:x$ student of your school $\} $

Which of the following are sets ? Justify your answer.

A collection of most dangerous animals of the world.

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

$\varnothing \subset A$

Examine whether the following statements are true or false :

$\{ a\}  \in \{ a,b,c\} $

In the following state whether $\mathrm{A = B}$ or not :

$A = \{ 2,4,6,8,10\} ;B = \{ x:x$ is positiveeven integer and $x\, \le \,10\} $

Write the following sets in the set-builder form :

${\rm{\{ 5,25,125,625\} }}$