Several compartmentalized chemical reactions occur during the aerobic respiration of a single molecule of glucose.

Which of the following statements regarding these reactions is/are correct?

1. Substrate-level phosphorylation occurs during both glycolysis in the cytoplasm and the Krebs cycle in the mitochondrial matrix.
2. For each molecule of glucose oxidized in aerobic respiration, the link reaction produces more molecules of carbon dioxide (${CO}_2$) than the Krebs cycle.
3. The accumulation of protons ($H^{+}$) in the intermembrane space creates an electrochemical gradient used to drive ATP synthesis via ATP synthase.