Which of the following is an example of a complex number that is not in the set of real numbers?

A complex number is not real when it has a nonzero imaginary part. Choice B, 4 plus 9i, has imaginary part 9, so it is not a real number. The other choices are real numbers: 2 plus the square root of 3, negative 7, and pi.

AI-written and checked against the verified answer.