Which of the following are examples of the null set

Set of even prime numbers

Which of the following are sets ? Justify your answer.

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

In the following state whether $A=B$ or not :

$A=\{a, b, c, d\} ; B=\{d, c, b, a\}$

Make correct statements by filling in the symbols $\subset$ or $ \not\subset $ in the blank spaces:

$\{ x:x$ is an even natural mumber $\}  \ldots \{ x:x$ is an integer $\} $

State which of the following sets are finite or infinite :

$\{ x:x \in N$ and $x$ is odd $\} $

Which of the following are examples of the null set

Set of odd natural numbers divisible by $2$