Final answer:
Dr. Josef Mengele performed biological experiments on twins during World War II, mainly targeting children. These experiments involved surgeries, exposure to diseases, and chemicals.
Step-by-step explanation:
Dr. Josef Mengele, a notorious physician in Nazi Germany, performed biological experiments on twins during World War II. These experiments included surgeries, exposure to diseases like typhus and malaria, and the use of chemicals. His victims were mainly children and included other vulnerable groups like pregnant women.