Hi Naval,
Thanks for this. Looking at the CC on page 20, it's stated that: A coenzyme OR metal ion covalently bound to the enzyme is a prosthetic group.
This means that prosthetic groups have two categories:
1) Inorganic metal ions required for enzyme function
2) Coenzymes, or organic molecules required for enzyme function
For the Altius Question, they mention that Zinc is bound to the enzyme. This means that Zn is a prosthetic group as it falls into catagory 1), but it is not a coenzyme because a coenzyme by definition should be an organic molecule, which Zn is not.
I hope this helps!
Katt