Which of the following is the empty set

Which of the following are examples of the null set

$\{ y:y$ is a point common to any two parallellines $\} $

Which of the following are sets ? Justify your answer.

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

Consider the sets

$\phi, A=\{1,3\}, B=\{1,5,9\}, C=\{1,3,5,7,9\}$

Insert the symbol $\subset$ or $ \not\subset $ between each of the following pair of sets:

$A \ldots C$

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 $C$

$\{0,1,2,3,4,5,6,7,8,9,10\}$