When oxygen is depleted, the citric acid cycle stops. what could we add to the system to restore citric acid cycle activity (other than oxygen)?

NAD+, FAD.

Explanation:

The citric acid cycle is popularly known as the Kreb's cycle. The cycle involve the oxidation of acetyl-CoA to produce energy. The Kreb's cycle is a chemical process that produces produces two carbon dioxide molecules,NADH,FADH2 and one ATP.

When oxygen is depleted, the citric acid cycle stops, apart from oxygen NAD+ and FAD could be added to the system to restore citric acid cycle activity. NAD+ acts as an electron acceptor.

Citric acid cycle/Kreb's cycle is an aerobic process that occurs in the mitochondria and produces thirty-six(36) ATPs.

the equation that correctly represent the reaction for formation of ammonia is

n2+ 3h2 → 2nh3 (answer d)

1 mole of nitrogen gas (n2) react with 3 moles of hydrogen gas (h2) to form 2 moles of ammonia ( nh3). this is in a process known as haber process were iron is used as a catalyst and reaction take place that a higher temperature and pressure. the process is exothermic hence energy is released.