Which among these elements is required for the action of enzyme nitrogenase an enzyme needed for biological nitrogen fixation?

The correct option is A $Zn$

Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an enzyme called nitrogenase. Many nitrogen-fixing organisms exist only in anaerobic conditions, respiring to draw down oxygen levels, or binding the oxygen with proteins.

So the correct option is '$Zn$'.