The oxidation state rarely shown by Bismuth is

Due to Lanthanoid contraction , size increases from Sb to Bi is smallIn 'Bi' nuclear attraction over outermost electrons is more. Thus the paired 'ns' electrons are reluctantto uncouple and participate in bonding . Due to this reason 'Bi' shows an ox. state '+3' (corresponding to ground state)And it is unstable in higher ox. state(+5)Compounds of 'Bi' in '+5' state (except BiF5) are unstable and undergo reduction to form stable compounds with '+3' state'Bi' being a metal rarely shows negative oxidation state (-3)