State which of the followings are null set?

State which of the following is a null set?

Which of the following is a null set?

Which of the following is a null set

Which of the following is a null set?

State which of the following sets are null set or singleton set: the set of natural numbers less than 1

State which of the following sets are null set or singleton set:the set of real roots of x + 1 = 0

State which of the following sets are null set or singleton set:the set of positive odd integers less than 3

State which of the following sets are null set or singleton set:the set of even prime numbers

State which of the following sets are null set or singleton set:the set of deserts in the Himalayan range