Which theory? The Arrhenius theory would be that all acids had a H^+. The Bronsted-Lowry theory is that an acid donates a proton. There are other theories.
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One feature of all acids is that they are capable of donating protons, which are hydrogen ions (H+). Acids are substances that have a pH value below 7 and can dissociate in water to release positively charged hydrogen ions. When an acid is dissolved in water, it donates these hydrogen ions to the water, leading to an increase in the concentration of H+ ions in the solution. This ability to donate protons is what distinguishes acids from other substances.
