Select the most dangerous pollutant
(a)CO
(b)${SO}_{2}$
(c)${NO}_{2}$
(d)${CO}_{2}$

Hint They are odorless, no taste, and toxic. When it combines with hemoglobin it forms carboxyhemoglobin. They are a strong reducing agent. They are widely used as an industrial fuel and used to remove rust from the surface to metals.

Complete answer:
Carbon monoxide (CO) is the most dangerous pollutant. They are formed when organic compounds are burned in the presence of oxygen. Exhaust gases from automobiles, engine fumes, fire smoke, and non-electric heaters are the foremost common source of carbon monoxide gas production. Carbon monoxide has positive and adverse effects on humans. Increased levels of carbon monoxide gas in red blood cells decrease the quantity of oxygen hemoglobin carries throughout the body. The effect is that vital organs just like the brain, nervous tissues, and therefore the heart doesn’t get enough oxygen to function properly.

Additional information:
Carbon monoxide when breathed is dangerous as it replaces oxygen in the blood and relieves oxygen from the heart, brain, and other important organs. In minutes, massive quantities of CO will overtake you all of a sudden, causing you to lose consciousness and suffocate. To avoid getting poisoned by carbon monoxide gas, proper preventive measures must be taken. Some of the preventive measures are given below.
-There should be enough ventilation in houses with plenty of traffics or factories in the area.
- CO Detectors should be utilized and kept near the source of CO.
- Sleeping near kerosene or a gas space heater should be stopped.
- The symptoms of Carbon Monoxide Poisoning should never be disregarded.

So, the correct answer is 'CO'.

Note: The CO concentration is in parts per million (ppm) measured. Health effects from about 1 to 70 ppm of CO exposure are unclear, but most people don't feel any symptoms. As CO rates rise above 150 to 200 ppm, there is space for disorientation, unconsciousness, and death. Breathing in pure oxygen is the only way to treat CO poisoning. The procedure increases blood oxygen levels and assists in keeping CO out of the body. The doctor will put an oxygen mask over the mouth and nose and ask to inhale it.