WHEN BASES ARE CLASSIFIED ACCORDING TO THEIR STRENGTH AND ACIDITY THEY ARE TAKEN IN THEIR AQUEOUS SOLUTION BUT, ONLY ALKALI DISSOLVES IN WATER THEN HOW CAN WE CLASSIFY THE BASES WHICH ARE NOT ALKALI?

there are 3 theories for classifying acid and bases, first is arrhenius theory, bronsted and lowry concept and lewis concept. according to arrhenius concept acid are those substance which gives H+ ion in aqueous solution and bases which give hydroxy ion in their aqueous solution. according to bronsted and lowry concept acids are those substance which gives proton (indirectly means H+ ion) and bases are those substance which accept proton. according to lewis concept lewis acid are those substance which can accept a lone pair of electron and lewis base are those substance which can donate lone pair of electron. using these three concept you can identify which substance is acid or base and also you can compare strength of bases using bronsted lowry concept in which when a base accepts a proton then it forms a conjugate acid and more stable a conjugate acid means more strong base because a stable conjugate acid means base have a strong tendency to accept proton which means more basic.