What things are alkali?

Alkali's are soluble bases.

Bases are the oxides of Groups (I) & (II) metal elements.

Taking

Group (I)

sodium oxide (Na2O) , this is a BASE .

It dissolved in water to for the hydroxide , an Alkali.

Na2O + H2O = 2NaOH an alkali.

However taking Group (II)

Calcium oxide (CaO), this is a BASE.

It is sparingly soluble in water to form the hydroxide , an Alkali.

CaO + H2O = Ca(OH)2 an alkali.