Which of the following is a common component of photochemical smog and is a reddish-brown gas with a pungent odor?

The common component of photochemical smog that is a reddish-brown gas with a pungent odor is Nitrogen Dioxide (NO2).

Here are the steps to answer this question:

1. Understand the question: The question is asking for a common component of photochemical smog that is a reddish-brown gas and has a pungent odor.

2. Recall knowledge about photochemical smog: Photochemical smog is a type of air pollution that is a mixture of various substances, including nitrogen oxides, volatile organic compounds, and ozone.

3. Identify the component: Among these substances, Nitrogen Dioxide (NO2) is known to be a reddish-brown gas with a pungent odor.

So, the answer is Nitrogen Dioxide (NO2).