Explanation:

All the statements are correct. 

Hemoglobin is the protein that makes blood red. It is composed of four protein chains, two alpha chains and two beta chains, each with a ring-like heme group containing an iron atom. Oxygen binds reversibly to these iron atoms and is transported through blood.
In fact, it is the haemoglobin that is responsible for the colour of the red blood cell. Haemoglobin contains a haem prosthetic group that has an iron atom at its centre. When the iron is bound to oxygen, the haem group is red in colour (oxyhameoglobin), and when it lacks oxygen (deoxygenated form) it is blue-red.
Carbon dioxide doesn't compete with oxygen in this binding process. However, carbon monoxide CO is a very aggressive molecule. It has a greater affinity for hemoglobin than oxygen does. It displaces oxygen and quickly binds, so very little oxygen is transported through the body cells.