Smog is A. Nothing but black smoke B. A combination of smoke and fog C. A liquid particle resulting from vapour condensation D. A solid particle, e.g., fllyash

The correct answer is: B. A combination of smoke and fog.

Smog is a mixture of smoke and fog. It is a form of air pollution that is caused by the burning of fossil fuels, such as coal and oil. Smog can be harmful to human health, as it can cause respiratory problems, heart disease, and cancer.

Option A is incorrect because smog is not just black smoke. It is a mixture of smoke and fog.

Option C is incorrect because smog is not a liquid particle resulting from vapor condensation. It is a mixture of smoke and fog.

Option D is incorrect because smog is not a solid particle, such as fly ash. It is a mixture of smoke and fog.