Question

In primordial atmosphere when the living organism evolved the respiration process was

• A. Anaerobic as it released more energy.
• B. Aerobic as it was more complex.
• C. Aerobic as it released more energy.
• D. Anaerobic because early atmosphere contained little or no oxygen.

Answer 1

The correct option is D Anaerobic because early atmosphere contained little or no oxygen.

In any case scientists are sure that the primordial atmosphere contained no free oxygen ($O_2$) and therefore ozone could not exist either. So, in primordial atmosphere, when the living organism evolved the respiration process was anaerobic, because early atmosphere contained little or no oxygen. Thus, option D is correct.
In primordial atmosphere, the respiration process was not aerobic. Thus, option B and C are wrong.
In primordial atmosphere, the respiration process was not anaerobic as it released more energy. Thus, option A is wrong.