What is photochemical smog?

What is smog? How is classical smog different from pholochemical smog?

Among the isomeric alkanes of molecular formula C_5H_12 identify the one that on photochemical chlorination yields. A single monochloride.

Among the isomeric alkanes of molecular formula C_5H_12 identify the one that on photochemical chlorination yields. Three isomeric monochlorides.

Among the isomeric alkanes of molecular formula C_5H_12 identify the one that on photochemical chlorination yields. Four isomeric monochlorides.

Mention the four important events/processes associated with the photochemical phase or light reaction of photosynthesis.