Good question!
For industrial use I would surmise that sulfuric acid is the most used acid in the world.
Still, with all the digestion going on in the world, a lot of hydrochloric acid is being used.
sulfuric acid
Sulfuric Acid
English
The acid of H2SO4 is sulfuric acid. It is a strong mineral acid with the chemical formula H2SO4. Sulfuric acid is commonly used in various industrial processes and is one of the most widely produced chemicals in the world.
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English is the most widely used second language in the world. It is an official or widely spoken language in many countries, and is commonly used as a lingua franca for international communication in business, tourism, and diplomacy.
The most widespread firearm is by far and away the AK-47, but the most widely used weapon? probably a simple knife/machete
The most widely traded spice in the world is black pepper. It is used in cuisines globally and is known for its strong flavor and aroma.
Mandarin has the most number of native speakers and English is the most widely spoken.
Mandarin has the most number of native speakers, but English is the most widely used langague in the world.
The Euro is the most widely used currency in Europe and the world for that matter.
Caffeine is the most widely used psychotropic drug in the world. It is found in coffee, tea, and many other beverages and foods.