When an antigen is administered for the first time to an animal or a human being who has never been exposed to it, the first antibody to develop -

IgM is a heavy molecule. IgM molecules are polymers of five four-peptide subunits. - IgM antibodies are relatively sho-liveddisappearing earlier than IgG. hence their demonstration in serum indicates recent infection. RefReference:athanarayan & paniker's 9th edition, pg no: 98 <\p>