The Empty Set

The correct answer is: (D):

We are tasked with identifying which of the following sets is an empty set. Let’s analyze each option:

Step 1: Examine the set

This set contains all real numbers that satisfy the equation . Let’s solve this equation:

There is no real number whose square is negative. Therefore, there are no solutions to the equation in the set of real numbers . This implies that the set is empty.

Step 2: Conclusion
Since no real number satisfies the given equation, the set is indeed an empty set.

Conclusion:
The correct answer is (D): , as it is the empty set.