What element is found in all acids?

• A. Oxygen
• B. Nitrogen
• C. Hydrogen
• D. Carbon

Answer: (C)

Acids are defined by their ability to donate a hydrogen ion to a base. Because this proton donation centers on hydrogen, the element found in all acids is hydrogen. For example, hydrochloric acid (HCl), sulfuric acid (H2SO4), and acetic acid (CH3COOH) all contain hydrogen that's released or used in the reaction. Oxygen, nitrogen, or carbon may appear in many acids, but they’re not universal to every acid—there are common acids that don’t require those elements. So hydrogen is the element present in all acids.