The number of non-empty subsets of the set $\{1, 2, 3, 4\}$ is

- A
$15$

- B
$14$

- C
$16$

- D
$17$

Write the following sets in roster form :

$\mathrm{E} =$ The set of all letters in the world $\mathrm{TRIGONOMETRY}$

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

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

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

$ 2 \, ....... \, A $

Which of the following are sets ? Justify your answer.

The collection of all natural numbers less than $100 .$

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

$\{ 3,4\} \in A$