The element often present in fuels which produces an acid gas after combustion is sulfur.

Here's why:

* Sulfur dioxide (SO2): When sulfur-containing fuels like coal or oil are burned, the sulfur reacts with oxygen to form sulfur dioxide (SO2).

* Acid Rain: Sulfur dioxide is a major contributor to acid rain. When SO2 dissolves in water droplets in the atmosphere, it forms sulfuric acid (H2SO4), which is a strong acid.

Let me know if you'd like to know more about acid rain!