Correct Answer: Carbon monoxide

Solution : The correct answer is carbon monoxide.

Carbon monoxide is a released on  the incomplete combustion of fuels. It is a tasteless, odorless and colourless gas which is toxic for human beings. It binds with haemoglobin in the blood and forms a stable compound known as carboxyhaemoglobin. Carbon monoxide has high haemoglobin affinity and it reduces the oxygen carrying capacity of blood, which turns life threatening.