Show that the set of letters needed to spell $"\mathrm{CATARACT}"$ and the set of letters needed to spell $"\mathrm{TRACT}"$ are equal.

Which of the following are sets ? Justify your answer.

The collection of all even integers.

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

$\{1,2,3\}\subset A$

Which of the following are sets ? Justify your answer.

A collection of most dangerous animals of the world.

State whether each of the following set is finite or infinite :

The set of letters in the English alphabet