Q.The compound which links glycolysis and Kreb's cycle is:

Glycolysis ends with pyruvate; pyruvate is then converted (via oxidative decarboxylation, releasing CO2 and NADH) into Acetyl CoA, which is the actual link molecule that feeds carbon into the Krebs (citric acid) cycle.

Tracing the pathway: Glycolysis (in the cytoplasm) breaks down one glucose molecule into two molecules of pyruvic acid (pyruvate). Under aerobic conditions, pyruvate enters the mitochondrial matrix, where the pyruvate dehydrogenase enzyme complex catalyses its oxidative decarboxylation: pyruvate loses one carbon as CO2, is oxidised, and combines with Coenzyme A to form Acetyl CoA (a 2-carbon acetyl group attached to CoA), generating NADH in the process. It is this Acetyl CoA — not pyruvate itself — that condenses with the 4-carbon oxaloacetate to form 6-carbon citrate, the first step of the Krebs cycle. This is why Acetyl CoA is described as the molecule that …