Let $A$ and $B$ be two non-empty subsets of a set $X$ such that $A$ is not a subset of $B$. Then:

Which of the following is an example of the null set?
Set of odd natural numbers divisible by $2$.

In this question,all integers are represented in base $10$. Consider the set $E$ of positive integers $n$ having the property that when any nonzero digit $d \in \{1, 2, \dots, 9\}$ is written to the right of $n$,the resulting number is divisible by $d$. Let $N$ be the smallest element of $E$. The product of the digits of $N$ is:

Examine whether the following statement is true or false:
$\{a\} \in \{a, b, c\}$

Make correct statements by filling in the symbols $\subset$ or $\not\subset$ in the blank spaces:
${ x:x \text{ is an even natural number} } \dots { x:x \text{ is an integer} }$

In the following,state whether $A=B$ or not:
$A=\{a, b, c, d\} ; B=\{d, c, b, a\}$