Which characteristic is common to both acids and bases?

When either acids or bases are mixed with water, the resulting process is typically exothermic, meaning heat is released during the reaction. This occurs as hydrogen ions (H+) form hydronium ions (H3O+) in acids, and hydroxide ions (OH-) are released in bases. The other options apply to either acids or bases exclusively, not both: acids have pH less than 7 (bases have pH greater than 7); bases generally taste bitter while acids taste sour; and while some acids are used as preservatives, this is not a universal characteristic of both acids and bases.