Which substance is NOT associated with being a mutagenic agent?

Water is not associated with being a mutagenic agent, meaning it does not cause changes or mutations in the DNA of an organism. Unlike the other substances listed, water is a stable, necessary component for life and does not exhibit properties that are known to induce genetic mutations.

X-rays and UV light are types of radiation that can damage DNA. X-rays are high-energy electromagnetic radiation that has the ability to ionize molecules and disrupt cellular structures, leading to mutations. UV light can cause the formation of thymine dimers in DNA, which can result in errors during DNA replication. Mustard gas, a chemical warfare agent, is known for its mutagenic properties because it interacts with DNA and can lead to significant genetic damage.

In summary, while X-rays, UV light, and mustard gas can all induce mutations through various mechanisms, water remains a benign and essential substance that does not partake in mutagenic activities.