Write down all the subsets of the following sets
$\{ a,b\} $
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 ?
$\varnothing \in A$
Write the set $\{ x:x$ is a positive integer and ${x^2} < 40\} $ in the roster form.
Given the sets $A=\{1,3,5\}, B=\{2,4,6\}$ and $C=\{0,2,4,6,8\},$ which of the following may be considered as universal set $(s)$ for all the three sets $A$, $B$ and $C$
$\{ 1,2,3,4,5,6,7,8\} $