Which of the following air pollutants is quiet killer:

Explanation

Carbon monoxide is highly poisonous gas and causes suffocation if inhaled. It binds blood haemoglobin more strongly than oxygen thus excluding oxygen from normal respiration. The CO poisoning can be reversed by giving high pressure oxygen. Exposure to high concentration of CO results in headache, fatigue, unconsciousness and eventually death (if such exposure is sustained for longer period). It is a colourless and odourless gas hence there is no way to detect it in case of leakage etc. so it is called quiet killer.