Question

fermentation occurs just after the electron transport chain when oxygen is not available just after the krebs cycle only when oxygen is available

Explanation:

Fermentation is an anaerobic process. It occurs when oxygen is not available as cells seek an alternative way to generate energy. It is not directly related to the electron - transport chain's immediate aftermath, nor is it exclusive to after the Krebs cycle. It doesn't occur only when oxygen is available.

Answer:

when oxygen is not available