What is acids and bases?

the compounds which gives the H+ ions are called acids .the compounds which gives the OH- ions are called bases.

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According to Arhenius the compounds which gives H+ ions in water are called "acids" and the compounds which gives OH- ions in water are called "bases".

there are many theories explaining what are acids and bases like arrhenius theory ,lewis acid-base concept........the simple way to ans this qn is the compounds when dissolved in water which gives H+ ions are called acids and which gives OH- ions are called bases.....or compounds which have ph value <7 are called acids and compounds which have have ph>7 are called bases