The correct answer to the question is option 2: liver. The liver is the largest organ in the human body, weighing approximately 1.5 kilograms in an average adult. It is located in the upper right side of the abdomen, just below the diaphragm.

Option 1: The thyroid is a small, butterfly-shaped gland located in the lower front of the neck. While it plays a significant role in regulating metabolism, it is relatively small compared to the liver.

Option 3: The pancreas is a long, flat gland located behind the stomach. It is responsible for producing enzymes that aid in digestion and regulating blood sugar levels. Although important, it is smaller in size compared to the liver.

Option 4: The spleen is an organ located in the upper left side of the abdomen. It helps filter blood, store red blood cells, and fight infection. However, it is also smaller in size compared to the liver.

Therefore, the liver is the largest organ in the human body, making option 2 the correct answer.