The correct answer is option 1: Carbon Monoxide reacts with haemoglobin. Carbon Monoxide is a pollutant because it binds to the oxygen-carrying molecule called haemoglobin in our red blood cells. Haemoglobin normally binds with oxygen and carries it to different parts of our body. However, when carbon monoxide is present in the air, it competes with oxygen to bind with haemoglobin, forming a compound called carboxyhaemoglobin. This prevents haemoglobin from effectively carrying oxygen, leading to reduced oxygen supply to our organs and tissues. This can have serious consequences, as our bodies require oxygen for proper functioning. Breathing in high levels of carbon monoxide can result in symptoms like headache, dizziness, nausea, and even death in extreme cases. Therefore, carbon monoxide is considered a pollutant and a harmful gas.