COMEDK Exam 2015 Solved Paper

Due to −I and −R-effects of −NO2 group, nitrobenzoic acids are stronger acids, than benzoic acid Due to ortho-effect, o-nitrobenzoic acid is the strongest acid.
In p-nitrobenzoic acid both −R-effect and −I-effect of the −NO2 group increase the acidity, while in m-nitrobenzoic acid only the weaker −I-effect increases the acidity.
Hence, the order of acidic strength is o-nitrobenzoic acid >p-nitrobenzoic acid
>m-nitrobenzoic acid > benzoic acid.