Which chemical is commonly found in older transformers and is considered a cancer-causing agent?

Polychlorinated biphenyls (PCBs) are synthetic organic chemicals that were widely used in electrical transformers and other industrial applications until their harmful effects became known. PCBs are considered environmental pollutants and have been classified as probable human carcinogens by research studies.

These chemicals were favored for their insulating properties and electrical stability, making them ideal for use in transformers. However, over time, evidence has emerged linking PCB exposure to serious health issues, including various types of cancer.

Despite the presence of other hazardous materials like asbestos, lead, and mercury in older electronics, PCBs are particularly noted for their carcinogenic properties and long-lasting impact on human health and the environment, which is why they stand out as the correct answer in this context.