The enzyme nitrogenase is a (a) Cu-Fe protein(b) Ni-Fe protein(c) Mo-Fe protein(d) Ni-Cu protein

The correct answer is (c) Mo-Fe protein.

Explanation:

Nitrogenase is the enzyme responsible for the biological nitrogen fixation process, which converts atmospheric nitrogen (N2) into ammonia (NH3), a form that plants can utilize. Nitrogenase is a complex enzyme consisting of two main components:

Fe-protein (Iron protein) – contains iron and is involved in the transfer of electrons.
MoFe-protein (Molybdenum-iron protein) – contains molybdenum (Mo) and iron (Fe) and is the site of the actual nitrogen reduction reaction.
This MoFe-protein has a cluster of molybdenum and iron atoms that is crucial for its activity in fixing nitrogen. Therefore, nitrogenase is classified as a Mo-Fe protein.

Option (c) Mo-Fe protein is the correct choice.