The correct answer is option 4: Liver. The Liver is known as the Biochemical Laboratory of the Human Body because it performs a wide range of essential functions related to metabolism and detoxification.

The Liver plays a key role in breaking down and storing nutrients from the food we eat. It produces bile, which helps in the digestion and absorption of fats. Additionally, the Liver is involved in the synthesis of proteins, including clotting factors and immune molecules. It also metabolizes drugs and toxins, converting them into forms that can be eliminated from the body.

Although the other organs mentioned in the options (small intestine, brain, and pancreas) have important roles in the body, they do not have the same extensive range of metabolic functions as the Liver. Therefore, the Liver is commonly referred to as the Biochemical Laboratory of the Human Body.