Indicator theory and Acid-Base filtrations

According to Modern quinoid theory the indicator used in acid-alkali titrations are-

The rapid change of pH near the stoichiometric point of an acid-base titration is the basic of indicator detection. pH of the solution is related to the ratio of the concentration of conjugate acid (Hin) and base (In^(-)) forms of the indicator by the expression

The rapid change of pH near the stocichiometric point of an acid-base titration is the basis of indicator detrection. pH of the solution is related to the ratio of concentration of conjugate acid (HIn) to the concentration of base (In^(-)) froms of the indicator by the expression

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Which of the following acid-base reactions cannot be explained by the Bronsted theory ?

What is an indicator ? Name the indicators commonly used in acid base titrations and discuss the specific role played by them.