What is the oxidizing agent in the citric acid cycle that is derived in part from the vitamin niacin?

NAD (Nicotinamide adenine dinucleotide)

Explanation:

NAD + (or NADH in its reduced form) is important in cellular respiration as it acts as an electron carrier, providing a shuttle system for the movement of electrons. This drives a proton pump and generates ATP via oxidative phosphorylation. Niacin is a form of vitamin B3 that we get from our diet and is a precursor for NAD.