Which from following compounds has lowest thermal stability?

Why transition elements have more tendency to form interstitial compounds?

What is EAN of Co in $[\text{Co}(\text{NH}_3)_6]^{3+}$?

Identify the total number of complexes from following list having monodentate ligands in them
(a) Tetracyanonickelate (II) ion
(b) Potassium hexafluoroaluminate (III)
(c) Tetraamminecopper(II) ion
(d) Potassium trioxalatoaluminate (III)