Living in the atmosphere of CO is dangerous because it : 

1. Combines with O₂ present inside to form CO₂

2. Reduces organic matter of tissues.

3. Combines with haemoglobin and makes it incapable to absorb oxygen.

4. Dilutes the blood.

The reaction/s involved during the formation of photochemical smog are:

\(1. \space NO_2(g) \rightarrow NO(g) + \stackrel{\cdot}{O(g)}\)

\(2. \stackrel{\cdot}{O(g)} + O_2(g) \rightarrow O_3(g)\)

\(3.\space O_3(g) + NO(g) \rightarrow NO_2(g) + O_2(g)\)

4. All of the above

The incorrect statement about carbon monoxide is-