Which of the following sets are null sets

Which of the following sets are null sets

A

{x: |x |< -4, x ?N}

B

2 and 3

C

Set of all prime numbers between 15 and 19

D

{x: x < 5, x > 6}

Answer:

The correct option is B. 2 and 3

Note
2 and 3 is the null set.