Blood Looks Red Because of
Option 2 is the right answer.
Blood is red because it is made up of corpuscles that are red, which are called red blood cells. But, to understand why these cells are red you have to study them on a molecular level. Within the red blood cells there is a protein called hemoglobin. Each hemoglobin protein is made up subunits called hemes, which are what give blood its red color. More specifically, the hemes can bind iron molecules, and these iron molecules bind oxygen. The blood cells are red because of the interaction between iron and oxygen. (Even more specifically, it looks red because of how the chemical bonds between the iron and the oxygen reflect light.) And it’s very important for blood to be able to carry oxygen because when blood flows through the lungs, the blood picks up oxygen, and the blood carries this oxygen to the rest of the body until the oxygen is all used up — the blood then returns to the lungs to get more oxygen.