Answer: b. photochemical smog
Step-by-step explanation:
Photochemical smog is the most common type of smog. It is produced when the ultraviolet rays in sunlight reacts with the nitrogen oxides present in the atmosphere.
It can be seen as visible brown haze. It can be seen in morning and in afternoon. It can be seen in cities which are densly populated.
The largest contributor to the formation of photochemical smog are automobile emission, and coal power plants.