Photochemical smog primarily consists of a mixture of pollutants that react with sunlight. Here are explanations to each given options:

Option 1: Hydrocarbons. These are typically released by vehicles and industrial processes. They can contribute to smog, but they`re not produced during the formation of photochemical smog.

Option 2: Nitrogen Oxides. These are also contributors to smog, particularly in urban areas. However, like hydrocarbons, they aren`t produced during the formation of photochemical smog, rather they react in the presence of sunlight to form smog.

Option 3: Ozone. This is the correct answer. The key process in the formation of photochemical smog is the reaction between sunlight, nitrogen oxides, and volatile organic compounds. This reaction produces ozone, which forms the distinctive haze of photochemical smog.

Option 4: Methane. While methane is a powerful greenhouse gas, it does not play a significant role in the formation of photochemical smog.

So, Ozone is the product during the formation of photochemical smog.