The correct answer is option 2 - because of haemoglobin.
Human blood is red due to the presence of a protein called haemoglobin. Haemoglobin is responsible for carrying oxygen from the lungs to the rest of the body. It contains iron atoms that bind to the oxygen molecules. When oxygen attaches to haemoglobin, it gives blood a bright red color.
Option 1 - myoglobin is incorrect. Myoglobin is a related protein found in muscles, not in blood.
Option 3 - immunoglobin is also incorrect. Immunoglobulins, also known as antibodies, are produced by the immune system to help fight off infections. They are not responsible for the color of human blood.
Option 4 - heptoglobin is incorrect. Heptoglobin is a protein that binds to hemoglobin after it has been released from damaged red blood cells. It does not determine the color of blood.