Explanation

Pyruvic acid synthesized in glycolysis must enter inside the mitochondnia, where oxidative Decarboxylation occurs in presence of NAD⁺, pyruvic acid Dehydrogenase complex and coenzyme-A. Pyruvic acid + NA$D^{+}$ + Co-A $\overset{\rightarrow}{+ Co - A}$ Acetyl Co-A + $CO_{2}$+ NADH