The correct answer is option 3: Liver.

The liver is the largest organ in the human body. It is located in the upper right side of the abdomen, just below the diaphragm. The liver performs many important functions in the body, including filtering blood, detoxification of harmful substances, production of bile for digestion, and storage of certain vitamins and minerals.

Option 1, the heart, is an important organ responsible for pumping blood throughout the body but it is not the largest organ. Option 2, the brain, is the command center of the body but it is not the largest organ either. Option 4, the kidney, is responsible for filtering waste and excess fluid from the blood but it is also not the largest organ.