The conversion of malate to oxaloacetate in the citric acid cycle takes place with the conversion of NAD to NADH. In this reaction, NAD is:

oxidized.

destroyed.

the oxidizing agent.

reduced.

unchanged.

a) the oxidizing agent.

Explanation:

In the citric acid cycle, malate is dehydrogenated into oxaloacetate and the reaction is catalyzed by malate dehydrogenase. The released electrons are accepted by NAD+. So, NAD + is reduced into NADH. The substances that accept electrons during chemical reactions and are reduced to oxidize the other substances are called oxidizing agents. NAD + serves as an oxidizing agent as it accepts electrons to oxidize malate into oxaloacetate.