Which metal ion is a constituent of chlorophyll?

The correct option is D Magnesium
Iron:

Iron metal is found in the active site of various proteins such as hemoglobin, iron-sulphur proteins. Iron acts as an electron carrier in these proteins.

Copper:

Copper ion is present in proteins such as cytochrome, where it acts as an electron carrier.

Magnesium:

Magnesium ion is present in the centre of the chlorophyll molecule as $M{g}^{2+}$ ion.




Zinc:

Zinc is also present in the active site of many enzymes which are involved in protein synthesis.

Final answer:

c. Magnesium