Which of the following substances is defined as cancer-causing?

The term "carcinogen" specifically refers to any substance that can lead to cancer by causing changes in cellular DNA or inducing other biological processes that promote cancer development. Carcinogens can be physical agents, such as radiation, or chemical substances, such as certain types of benzene or asbestos. They may contribute to tumor formation through various mechanisms, including the promotion of mutations in critical genes responsible for regulating cell growth and division.

In contrast, antioxidants are compounds that help prevent oxidative stress and may reduce the risk of cancer by neutralizing free radicals. Mutagens are agents that can cause alterations in the genetic material of an organism, which can lead to mutations; however, not all mutagens are carcinogenic. Tumor suppressors are genes that help regulate cell division and prevent uncontrolled cell growth, and their loss or dysfunction can lead to cancer, but they are not substances that cause cancer themselves. Thus, the defining nature of a carcinogen as a cancer-causing agent clarifies why it is the correct choice in this context.