What would happen if oxygen availability to activated sludge flocs is reduced?

Activated sludge flocs have bacteria which are aerobic (i.e., oxygen breathing) organisms. If oxygen availability to activated sludge is reduced then the center of flocs will become anoxic, which would cause death of bacteria and eventually break the flocs.

The other options are incorrect. Thus, option b. The center of flocs will become anoxic, which would cause death of bacteria and eventually breakage of flocs is the correct answer.