Which of the following acid does not exhibit optical isomerism?
(a) Maleic acid (b) -amino acid
(c) Lactic acid (d) Tartaric acid
(a) Only those compounds exhibit optical isomerism, which have chiral centre and/or absence of symmetry elements. (Chiral carbon is the carbon in which all the four valencies are satisfied by four different groups.)
(one chiral centre,
so, optically acid)
Thus, maleic acid does not exhibit optical isomerism.