Final answer:
Cytotoxic T cells, also known as killer T cells, are responsible for killing abnormal or virus-infected cells by inducing apoptosis.
Step-by-step explanation:
The type of lymphocyte responsible for killing abnormal or virus-infected cells is the cytotoxic T cell. Cytotoxic T cells, also known as killer T cells, are a type of white blood cell that plays a vital role in the cell-mediated immune response. They destroy virus-infected cells by inducing apoptosis, the process of programmed cell death. For example, if a cell has been infected with a virus, cytotoxic T cells will recognize that cell as abnormal and release special proteins called perforins and granzymes to target and kill the infected cell.