Alkali
In chemistry, an alkali (; from Arabic: "al-qaly" "ashes of the saltwort") is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Alkali hydroxide
The alkali metal hydroxides are the strongest of all bases.The order of basicity increases down the group, i.e., LiOH is the least basic and CsOH, the most basic hydroxide. It is due to the property of bases to donate ion and due to small size and high lattice enthalpy of Li, it donates less and large size and low lattice enthalpy of Cs, Cesium hydroxide donates more ions than any other hydroxide. All the alkali metal hydroxides are white crystalline solids and dissolve freely in water with evolution of much heat.