Alkalis are a class of chemical compounds that are capable of absorbing hydrogen ions. Such as metal oxides or hydroxides are alkalis. The water-soluble alkali that provides hydroxide ions ( OH−) is called alkali according to the Bronsted-Laurie theory. Other theories or definitions of bases include electron pairing , source of hydroxide ions or Arhenius theory. These chemical compounds dissolve in water and release hydrogen ions, making the pH of the solution higher than that of plain water. Notable among the most common bases are sodium hydroxide , ammonia.