What is the coordination number of the central metal ion in the $[Co(en)_3]^{3+}$ complex?

In a complex compound, the central metal ion acts as a:

According to $Werner's$ theory for coordination compounds,which of the following is true?

The oxidation state and covalency of $Al$ in $[AlCl(H_2O)_5]^{2+}$ respectively are

Identify the total number of complexes from the following list that contain only monodentate ligands:
$(a)$ $[Ni(CN)_4]^{2-}$ (Tetracyanonickelate $(II)$ ion)
$(b)$ $K_3[AlF_6]$ (Potassium hexafluoroaluminate $(III)$)
$(c)$ $[Cu(NH_3)_4]^{2+}$ (Tetraamminecopper$(II)$ ion)
$(d)$ $K_3[Al(C_2O_4)_3]$ (Potassium trioxalatoaluminate $(III)$)

Which one is a Homoleptic complex?