Find the coordination number of Co in $[Co(Cl)(en)_2]Cl$

• The species inside the coordination sphere is $[Co(Cl)(en)_2]^+$.
• Here:
  • $Cl^-$ inside the bracket is a monodentate ligand, so it donates 1 pair.
  • $en$ (ethane-1,2-diamine) is a bidentate ligand, so each $en$ contributes 2 coordination sites.
• Since there are $2$ $en$ ligands, total from $en$ is: $2 \times 2 = 4$
• Adding the one $Cl^-$ ligand: $4 + 1 = 5$

So, the coordination number of Co is 5.

Find the coordination number of Al in $K_3[Al(C_2O_4)_3]$

• The complex ion is $[Al(C_2O_4)_3]^{3-}$.
• Oxalate, $C_2O_4^{2-}$, is a bidentate ligand.
• There are $3$ oxalate ligands, so total coordination sites are: $3 \times 2 = 6$

So, the coordination number of Al is 6.

Match with the options

• Co $= 5$
• Al $= 6$

Hence the correct option is: $\boxed{\text{D: } 5 \text{ and } 6}$

Comparison with stored correct answer

• Stored correct answer: D
• Derived answer: D

They match.