Final answer:
The gas described is likely sulfur dioxide (SO₂), which is a yellowish-brown to reddish-brown foul-smelling gas. It is emitted from industrial processes and is a major contributor to smog and acid rain.
Step-by-step explanation:
The gas described, greenish/yellow with a penetrating odor and is heavier than air, is likely sulfur dioxide (SO₂), which is a yellowish-brown to reddish-brown foul-smelling gas. Sulfur dioxide (SO₂) is one of the highly reactive gases known as oxides of sulfur. It is emitted from industrial processes and is a major contributor to smog and acid rain.
Chemistry keywords: sulfur dioxide, SO₂, gas density, pollution