Which of the following are sets ? Justify your answer.

The collection of all boys in your class.

For an integer $n$ let $S_n=\{n+1, n+2, \ldots \ldots, n+18\}$. Which of the following is true for all $n \geq 10$ ?

In rule method the null set is represented by

Write the following sets in the set-builder form :

$\{ 1,4,9 \ldots 100\} $

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

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

Write down all the subsets of the following sets

$\{ a,b\} $