Sulfuric acid is the most important industrial acid. Its chemical formula is H2SO4. Any industrial society on Mars will produce tonnes of the stuff, as it is used in countless chemical and industrial reactions.
Sulfuric acid on Mars could be a by-product of copper production, or of regolith mineral processing for magnesium, calcium or other metals . Sulfur is very common in the Martian lithosphere. In the form of SO3 it can represent up to 37% by weight of certain rock formations. SO3 + H2O can produce sulfuric acid, although not directly in an industrial process as the reaction is too exothermic.
The washing of iron sulfides, common on Mars, with liquid water could also be a source of sulfuric acid.
Sulfuric acid is mainly used on Earth for producing fertilizers (60%), industrial regents and plastics. It is also used in making steel, mostly as a cleaning agent and surface preparation role. Sulfuric acid in steel making plants is usually recycled at the plant.
Sulfuric acid is combined with ammonia, and therefore Nitrogen, to produce ammonium sulfate fertilizers. It can also be used to produce explosives for mining when combined with suitable fuels.