a) When there is abundant NADH, it readily gets reduced and continues to give electrons to the carriers, which make all carriers to reduce, but when Oxygen is exhausted, there will be no oxygen for re-oxidizing the reduced carriers. b) when oxygen is abundant and NADH is exhausted, all the carriers which get reduced previously will be re-oxidized and stays the same. c) addition of rotenone, blocks the electron transfer from Complex I to CoQ. Complex I is responsible for NADH Dehydrogenation and reduction of the immediate acceptor carrier. when this is blocked, NADH will be in a reduced state, while the other carriers will be in an oxidized state. Solution a) When there is abundant NADH, it readily gets reduced and continues to give electrons to the carriers, which make all carriers to reduce, but when Oxygen is exhausted, there will be no oxygen for re-oxidizing the reduced carriers. b) when oxygen is abundant and NADH is exhausted, all the carriers which get reduced previously will be re-oxidized and stays the same. c) addition of rotenone, blocks the electron transfer from Complex I to CoQ. Complex I is responsible for NADH Dehydrogenation and reduction of the immediate acceptor carrier. when this is blocked, NADH will be in a reduced state, while the other carriers will be in an oxidized state..