The correct answer is option 3: Smallpox. Smallpox is the disease that has been eradicated, which means it no longer exists in the world. It was a highly contagious and deadly disease caused by the variola virus. Smallpox caused severe symptoms such as high fever, rash, and blisters all over the body. It was responsible for millions of deaths throughout history. However, due to global vaccination efforts, the World Health Organization (WHO) declared smallpox eradicated in 1980. This is a significant achievement in public health as smallpox is the only disease to be eradicated so far. It is important to note that while diseases like mumps, measles, and chickenpox can be prevented through vaccination, they have not been completely eradicated.