Which of the following is NOT an example of a mutagen?

A mutagen is an agent that causes changes or mutations in the DNA sequence, which can lead to genetic alterations in organisms. X-rays, cosmic rays, and ultraviolet rays are all forms of radiation that have enough energy to damage DNA, and they can lead to mutations by inducing breaks in DNA strands or causing incorrect base pairing during DNA replication. These types of radiation increase the risk of cellular damage and are recognized as mutagens in various biological contexts.

In contrast, Vitamin C is a nutrient that plays an important role in various physiological functions, such as acting as an antioxidant. It does not have mutagenic properties and is not known to cause changes in DNA structure. Therefore, Vitamin C is clearly not classified as a mutagen, making it the correct answer in this context.