Which from following ligands is able to form linkage isomers?

Identify the total number of complexes having bidentate ligands in them from following list of complexes.

a) Tetracyanonickelate(II) ion

b) Trioxalatocobaltate(III) ion

c) Sodium hexafluoroaluminate(III)

d) bis(ethylenediamine)dithiocyanatoplatinum(IV)

Identify neutral sphere complex from following.

Identify a ligand having two donor atoms but uses a pair of electrons of either donor atom to form coordinate bond.