With regard to the Biological Nitrogen Fixation by Rhizobium in association with soyabean, which one of the following statement/statements does not hold true?
1. Nitrogenase may require oxygen for its functioning .
2. Nitrogenase is MO-Fe protein.
3. Leg-hemoglobin is a pink coloured pigment.
4. Nitrogenase helps to convert ${\mathrm{N}}_2$ gas into two molecules of ammonia. 

In plants with nitrogen fixing bacteria (such as alfalfa or soybeans), the presence of oxygen will poison the bacterium. Which of the following acts as a natural defense against oxygen toxicity by scavenging free oxygen in these systems?

For biological fixation of one molecule of nitrogen into two molecules of ammonia, the number of ATP molecules needed is: