Answer:
Moderate reaction means those reactions which proceed with a measurable rates at the normal room temperature.
Answer : The equilibrium will shift in the left direction.
Explanation :
Le-Chatelier's principle : This principle states that if any change in the variables of the reaction, the equilibrium will shift in the direction to minimize the effect.
The given reaction is:

As per question, when we are adding
then the concentration of
is increased on product side then the equilibrium will shift in the direction where decrease of concentration of
takes place. Therefore, the equilibrium will shift in the left direction.
Thus, the equilibrium will shift in the left direction.
B.
The cynobacteria were already there without the oxygen, so that rules out A, and a lot of prokaryotes were anaerobic, so that rules out C. Finally, Photosynthesis does not require oxygen. Instead, Oxygen is a waste product of it. Therefore, it cannot be D. So, we are only left with B
Hoped this helped :D