An amino acid is characterized by two pKa values the one corresponding to the more acidic site is designated as `pKa_1` and the other corresponding to the less acidic site is designated as `pKa_2` The isoelectric point also called isoionic point (pI) is the pH at which concentration of zwitter ion is maximum . pI is the average of `pKa_1` and `pKa_2`.Generally the value of pI is slightly less than 7. some amino acids have side chain with acidic or basic groups.These amino acids have `pKa_3` value also for the side chain.Acidic amino acid have acidic side chains and basic amino acids have basic side chains . pI for acidic amino acid is average of `pKa_1 and pKa_3`.pI for basic amino acid is the average of `pKa_2 and pKa_3`. `{:(S.NO,"Amino acid",p^(Ka1),p^(Ka2),p^(Ka3)("side chain")),(I,"Aspartic acid",1.88,9.6,3.65),(II,"Glutamic acid",2.19,9.67,4.25),(III,"Lysine",2.18,8.95,10.53),(IV,"Arginine",2.17,9.04,12.48):}` In the table given above the acidic amino acids areA. I,IIB. I,IIIC. II,IIID. I,II, IV