Antibodies are formed in the lymph nodes. Lymph nodes are small, bean-shaped organs located all throughout the body, especially in areas such as the neck, armpit, and groin. These nodes are a part of the lymphatic system, which plays a vital role in the body`s immune response.

Option 2, the red bone marrow, is responsible for producing various types of blood cells, including immune cells, but the formation of antibodies primarily occurs in the lymph nodes. The marrow is involved in the maturation of some immune cells, but not the production of antibodies.

Option 3, the spleen, is an organ that acts as a filter for blood, removing old or damaged red blood cells. While the spleen does play a role in the immune system, it is not the primary site for antibody formation.

Option 4, the liver, is involved in many essential functions in the body, such as detoxification and nutrient storage, but it is not directly involved in antibody production.

Therefore, the correct answer is option 1, the lymph nodes. Antibodies are formed in the lymph nodes as a part of the immune response when the body encounters pathogens or foreign substances.