Acids

Lavoisier and Davy studied the terms acids bases and salts.
Acids:
 “Acid” word derived from the Latin word “Acidus” means SOUR.
 Compulsorily have hydrogen
 H⁺ is present in the form of H₃O⁺ when dissolved in water.
 Turns Blue litmus red
Definition:
Acids are defined as the compounds which contain one or more hydrogen atoms and when dissolved in water, produce hydronium ions (H3O+), the only positively charged ions.
Examples: Hydrochloric acid (HCl), Sulphuric Acid (H2SO4), Nitric Acid (HNO3), Acetic Acid (CH3COOH) etc.
According to the ionic theory, an acid is a compound which, when dissolved in water yields hydronium ions (H3O+)as the only positively charged ions.
HCl →  H⁺ + Cl- (Chloride ion)

H⁺ + H₂O → H₃O⁺ (Hydronium ion or simply H⁺)