EDTA ^ 4 - is ethylenediaminetetraacetate ion. The total number of...

${EDTA}^{4 -}$ is a hexadentate ligand containing four negative charges on its corner oxygen atoms as follows :

Being a hexadentate ligand, it forms a ring like structure through chelation.

The central metal ion $Co$ is in the centre, coordinated to the two $N$ atoms and the four ${O}^{-}$ ions through chelation. Now, if we observe, we see that each $N$ atom forms four $N - Co - O$ bonds with the four ${O}^{-}$ ions. Therefore, two $N$ atoms will form $2 \times 4 = 8$ $N - Co - O$ bonds in the complex structure of $[ Co ( EDTA ) {]}^{1 -}$. Each bond will have a certain bond angle. Hence, it can be concluded that the total number of $N - Co - O$ bond angles in the complex ion is $8$.