The correct answer is option 2, Liver.

1. Adrenal: The adrenal glands are endocrine glands located on top of the kidneys. They produce hormones like cortisol, adrenaline, and aldosterone.

2. Liver: Although the liver has multiple important functions in the body, it is not considered an endocrine gland. Its main functions include detoxifying harmful substances, producing bile for digestion, and storing nutrients.

3. Pancreas: The pancreas is an endocrine gland that produces hormones such as insulin and glucagon, which regulate blood sugar levels. It also has exocrine functions, producing digestive enzymes.

4. Thymus: The thymus is a small endocrine gland located in the upper chest. It is responsible for the development of T-lymphocytes, which are essential for immune system function.

In summary, while options 1, 3, and 4 are all endocrine glands, the liver is not. It is an important organ, but it primarily performs exocrine and metabolic functions rather than endocrine functions.