The correct answer is option 1: protein. Haemoglobin is a protein that is found in red blood cells and is responsible for carrying oxygen from the lungs to the different tissues and organs in the body. It consists of four subunits, each containing a heme group that binds to oxygen molecules. Proteins are large molecules made up of amino acids, and they play various roles in the body such as enzymes, structural components, transport molecules, and antibodies. Carbohydrates, on the other hand, are molecules that serve as a source of energy, while fats are another source of energy and play a role in insulation and protection. Vitamins are organic compounds that are required in small amounts for various biological processes in the body. Therefore, haemoglobin is a protein and not a carbohydrate, fat, or vitamin.