Many co-enzymes are derivatives of which of the following?

The presence of ......... is required for the activity of carbonic anhydrase.

Enzyme enolase catalyzes the conversion of $2$-$PGA$ to Phosphoenolpyruvic acid in the presence of . . . . . . which is the cofactor.

The non-protein part of an enzyme is called:

Which one of the following metallic ions does not occur as a prosthetic group in any enzyme?

The enzyme cytochrome oxidase contains which of the following metal ions?