Isoelectric point is when

Ans: a (Net charge of protein is zero)Ref: Vasudevan & Sreekumari, 6th edi., Pg. 22Amino acids can exist as ampholytes or zwitter ions in solution, depending on the pH of the medium.Amino acids that contain an equal number of ionizablegroups of opposite charge and that therefore bear no netcharge are termed zwitter ions.The pH at which the molecule carries no net charge is known as iso-electric point or iso-electric pH (pI) At isoelectric point, the number of anions and cationspresent on protein molecule will be equal and net charge iszero.At iso-electric point the amino acid will carry no net charge,all the groups are ionized but the charges will cancel eachother. Therefore at iso-electric point, there is no mobility inan electric field.Solubility, viscosity and buffering capacity will be minimum at iso-electric point and precipitation will be maximum at pIpI of albumin is 4.7, casein is 4.6, haemoglobin is 6.7 & myoglobin is 7.