2. Why is nitrate (NO3-) a better electron acceptor than fumarate?3. Is NADH a better electron acceptor than H2

Nitrate (NO3-) is a better electron acceptor than fumarate because it has a more positive reduction potential. The reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. The more positive the reduction potential, the greater the species' affinity for electrons and thus its effectiveness as an electron acceptor. Nitrate has a reduction potential of +0.42V, while fumarate has a reduction potential of +0.03V. Therefore, nitrate is a better electron acceptor.

NADH is not a better electron acceptor than H2. In fact, it's the other way around. NADH is an electron donor. It has a negative reduction potential, which means it tends to lose electrons rather than gain them. On the other hand, H2 can act as an electron acceptor in certain reactions, such as in the presence of oxygen in aerobic respiration.