The correct option is C Serum albumin
Haemoglobin is a protein molecule that is found in the red blood cells. It is a metalloprotein as it contains Fe. It is a transport protein as it helps in the transportation of oxygen from lungs to the body tissues and carbon dioxide from body tissues to the lungs. It is made up of 4 polypeptide chains- 2⍶ and 2ꞵ chains.
Prothrombin is a protein synthesized in the liver. It is required in blood clotting.
Serum albumin is found in the blood and hence also known as blood albumin. It is the most abundant protein in human blood. It is synthesized in the liver, is monomeric and water soluble. Mosquitoes drink human blood because they require serum albumin from human blood to synthesize their eggs.
Serotonin is a primary amino compound mainly found in the brain, bowels and blood platelets.