For its activity, nitrogenase requires

The correct option is A high input of energy
$\text{Nitrogenase enzyme}$

An enzyme which is involved in biological nitrogen fixation is called nitrogenase. It converts atmospheric nitrogen to ammonia.

Nitrogenase enzyme requires a high input of energy in the form of ATP binding and hydrolysis to catalyse the reduction of atmospheric nitrogen.

$\text{Final answer}$

(d) high input of energy