Option 1: Diabetes is not a communicable disease. It is a chronic condition that affects the way our bodies metabolize sugar.

Option 2: Diphtheria is the correct answer. Diphtheria is a contagious bacterial infection that mostly affects the nose, throat, and sometimes the skin. It spreads from person to person through respiratory droplets or direct contact with infected individuals.

Option 3: Arthritis is not a communicable disease. It refers to inflammation of the joints, which can be caused by various factors such as age, genetics, or injury.

Option 4: Cancer is not a communicable disease. It is a group of diseases characterized by the uncontrolled growth of abnormal cells in the body. Cancer is not contagious and cannot be transmitted from person to person.

In summary, diphtheria is the only communicable disease among the given options. It is important to understand the difference between communicable and non-communicable diseases to prevent the spread of infectious illnesses.