If Hunds rule is not obeyed by some elements given below then which atom has maximum magnetic moment :

The correct option is B $Mn$
According to Hund's rule electrons are distributed among the orbitals of subshell in such a way as to give maximum number of unpaired electron with parallel spin. i.e. in a subshell pairing of electron will not start until and unless all the orbitals of that subshell will get one electron each with same spin.
So, only Mn have one unpaired electron and they have same magnetic moment while others have zero.