How do you find the number of attachment possible?

[Zsanielle Moncayo 1E]

In the second practice quiz for quiz 3 how is it found that (en) has two possible attachments? Is this based of the lone pairs? If so how does oxalato have 2 possible attachments of it has 10 lone pairs? Thank you!

[Monica Habashy 3A]

ethylenediammine it's a bidentate because it has 2 nitrogens. Each nitrogen is bound to only 2 hydrogens which means they have a lone pair of electrons that can bond to the transition metal.

[Jasmine Cha 1A]

Does this mean that whenever en is used you count it as 2 coordination numbers? Also, is dien also 2?

[Melanie_Wong_1K]

Ethylenediamine (en) is a bidentate which means it has 2 attachment sites.
Diethylenetriamine (dien) is a tridentate which means it has 3 attachment sites.

In the table on page 117 of the course reader, I believe every other ligand is a monodentate which means it has one attachment site except except for those with asterisks which are noted as *POLYDENTATE (CHELATE) at the bottom.