Which of the following substances is classified as a carcinogen?

Asbestos is classified as a carcinogen due to its fibrous mineral properties that, when inhaled or ingested, can lead to serious health issues, including various forms of cancer such as mesothelioma and lung cancer. Asbestos has been widely studied, and its carcinogenic potential is recognized globally; exposure to asbestos fibers can cause cellular damage that leads to cancer development over time. This significant health risk is why it has been regulated or banned in many countries.

In contrast, water is essential for life, and while impurities in water can be harmful, the substance itself is not considered a carcinogen. Oxygen, also vital for life, is not classified as a carcinogen, though excessive levels can create hazardous conditions in certain environments. Caffeine, a common stimulant found in coffee and tea, has not been classified as a carcinogen, and moderate consumption is generally considered safe. Overall, the classification of asbestos as a carcinogen is critical in understanding occupational health and safety standards in environments where exposure may occur.