Final answer:
Activated cytotoxic T-cells release perforin to fight a viral infection, which leads to the destruction of infected cells.
Step-by-step explanation:
The chemical released by activated cytotoxic T-cells to fight a viral infection is known as perforin. Perforin is a protein that forms pores in the membranes of infected cells, leading to cell death and thereby helping to eliminate the infection. Cytotoxic T-cells, which are a critical component of the adaptive immune system, recognize and kill virally infected cells to prevent the spread of viruses within the body.