A. Vinegar is the common name of acetic acid.
B. Rancidity is the result of the fat oxidising and butter can be kept out without going rancid because of salt and in rancid butter enzyme lipase breaks down into glycerol and butyric acid.
C. Formic acid is present in bee sting.
D. Lactic acid accumulates in sour milk.
E. Apples contain maleic acid which is cis-butenedioic acid and is a dicarboxylic acid.