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

$\{ x:x$ is a triangle in a plane $\}  \ldots \{ x:x$ is a rectangle in the plane $\} $

Which of the following are sets ? Justify your answer.

A collection of most dangerous animals of the world.

Write the following intervals in set-builder form :

$\left( {6,12} \right]$

Write the following sets in the set-builder form :

$\{ 2,4,6 \ldots \} $

State which of the following sets are finite or infinite :

$\{ x:x \in N$ and $x$ is odd $\} $