In the given complex [Fe(H2O)5NO]SO4 , the oxidation state of Fe is +1, as charge on NO is +1. In the presence of strong field ligand, the single electron in 4s orbital pairs up with 3d electron. Therefore the electronic configuration is Fe+ = 3d64s1 3d :
↑↓
↑↓
↑
↑
↑
4s :
3 unpaired electrons Hence, the complex is paramagnetic due to the presence of three unpaired electrons.