Which of the following is a carcinogen?

• A. Benzene
• B. Water
• C. Ammonia
• D. Oxygen

Answer: (A)

Understanding what makes a substance a carcinogen means looking at its ability to cause cancer, typically by damaging DNA or promoting abnormal cell growth. Benzene has strong evidence linking long-term exposure to an increased risk of blood cancers, especially leukemia, because its metabolites can damage bone marrow and disrupt normal blood cell formation. Health authorities classify benzene as a known human carcinogen, meaning there is clear evidence it can cause cancer in people.

Water, ammonia, and oxygen aren’t considered carcinogens in this context. Water is essential for life and doesn’t have a cancer-causing mechanism at normal exposure levels. Oxygen is also essential and, while reactive oxygen species can contribute to cellular damage, it isn’t categorized as a carcinogen. Ammonia is mainly an irritant and corrosive; it can cause acute injuries but isn’t classified as a cancer-causing substance based on current evidence.