Correct Answer: Carbon monoxide

Solution : The correct answer is carbon monoxide.

Carbon monoxide is a harmful colourless gas which is released by the incomplete combustion of fossil fuels in automobiles. It is harmful for human beings as it has high affinity with haemoglobin molecules and forms a stable compound, which decreases the oxygen carrying capacity of the blood. It is released from automobile exhaust, industries etc. Other gases released from automobiles are carbon dioxide, Sulphur dioxide and nitrogen oxides.