It is said that 4-methylbenzoic acid will be a weaker acid than benzoic acid. 4-nitrobenzoic acid will be a stronger acid than benzoic acid.
I don't understand why the methyl group on 4-methylbenzoic acid would affect the acidity. I know that it has an inductive effect (hyperconjugation) but I thought induction only had an effect over a one to two carbon distance. The carboxylic acid is separated from the methyl group by four carbons.