The correct option is C The number of ligands around a metal ion bonded by both σ and πbonds
The co-ordination number of a central metal in a complex is not determine through the number of only anionic ligands bonded to the metal ion bonded but also by π bonds and the number of ligands around a metal ion bonded by both σ and π bonds. So, correct options are (a), (b) and (c).