b) Oxidative.
The conversion of pyruvate to acetyl CoA in the tricarboxylic acid cycle is an oxidative process, as it involves the removal of a carbon dioxide molecule and the transfer of electrons to NAD+ to form NADH. This reaction is catalyzed by the enzyme pyruvate dehydrogenase and is a critical step in linking glycolysis (which produces pyruvate) to the tricarboxylic acid cycle (which generates energy through oxidative metabolism).