Which of the following is a set? Justify your answer.
The collection of questions in this chapter.

The set $A = \{ x : x \in \mathbb{R}, x^2 = 16 \text{ and } 2x = 6 \}$ is equal to

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:

The set $A = \{ x : x \ne x \}$ represents:

Which of the following is an empty set?

Which of the following are sets? Justify your answer.
The collection of all natural numbers less than $100$.