Ligand(s) with lone pair of elecftron(s) with vacant orbital to receive back the electrons donated to the metal is/are

What is a lone pair of electrons ?

A lone pair of electrons in an atom implies

A lone pair of electrons in an atom implies

The pi acid ligands donate their lone pairs to the metal to form a normal o bond with the latter in addition to it the vacant orbitals accepct electrons from the filled mental orbitals to form a type of pi bonand which suppliments the o bond Which of the following has lowest M-C bond lenght? [Ni(CO)_(4)] (b) [Mn(CO)_(6)]^(o+) (c) [Fe(CO)_(4)]^(2-) (d) [Co(CO)_(4)]^(Θ) .