The right answer is NAD+ is reduced (to NADH).
In a very large number of oxidation-reduction reactions that take place in the cell, the electrons are transferred by coenzymes: for example, nicotinamide adenine dinucleotide or NAD +.
they contain nicotinamide which is the amide of nicotinic acid
they contain a phosphoanhydride bond that links two nucleotides: adenosine monophosphate, which comes from ATP, and the nicotinamide ribonucleotide called nicotinamide mononucleotide
The NADH that is produced by the catabolic oxidation reactions is retransformed into NAD + under aerobic conditions with concomitant production of ATP: this is oxidative phosphorylation. NADH is therefore linked to reactions of catabolism (degradation reactions). It represents an energy source prior to ATP.
