(a) Base is a compound that contains displaceable oxide () or hydroxide () ion or ions. A base reacts with or ions (hydronium) present in an acid to produce a salt and water. Examples include NaOH and CuO.
(b) An alkali is a basic hydroxide that is soluble in water; it produces hydroxyl () ions as the only negatively charged ions. Sodium hydroxide and calcium hydroxide are water-soluble bases; thus, they are alkalis. But all bases are not alkalis, as many bases do not dissolve in water. Bases like ferric hydroxide and cupric hydroxide are not soluble in water; hence, they are not alkalis. Thus, we can say that all alkalis are bases, but all bases are not alkalis.