What are the two substances that may be formed in anaerobic respiration?

This has to depend on the type of anaerobic respiration.

for anaerobic respiration in human, such as the muscles while working out, lactic acid and energy may be formed. But in anaerobic respiration of yeast, ethanol, carbon dioxide and energy is formed instead. Both of these are very different but one thing in common is they release energy, as know as ATP.

anaerobic respiration means the chemical reactions that can generate energy for organisms without the presence of oxygen, unlike aerobic respiration. But note that in human, anaerobic respiration also creates an oxygen debt, and that's why we seem to breathe harder after exercise, we need to breathe in more oxygen.