In hepatitis, the organ of the body that is mainly damaged is the liver. Hepatitis is an inflammation of the liver that can be caused by viruses, alcohol abuse, autoimmune diseases, or certain medications. The liver plays a vital role in our body as it is responsible for filtering blood, detoxifying harmful substances, storing nutrients, and producing bile.

Option 1: Kidney - The kidney is not primarily affected in hepatitis. The kidney has its own set of functions, such as filtering waste from the blood and balancing electrolyte levels.

Option 2: Spleen - The spleen is not the primary organ affected in hepatitis. The spleen is involved in filtering the blood, destroying old or damaged red blood cells, and producing antibodies.

Option 4: Lung - The lung is not the organ primarily affected in hepatitis. The lung is responsible for exchanging oxygen and carbon dioxide during breathing.

Therefore, option 3 - liver is the correct answer. It is important to note that hepatitis can result in liver damage, and if not managed properly, it can lead to serious complications such as cirrhosis or liver failure.