Redox basics — In biochemical terms, oxidation is defined as the…

Introduction / Context:
Oxidation–reduction (redox) reactions underpin energy capture in metabolism. Remembering the core definitions helps track electron flow in pathways like respiration and fermentation. The mnemonic “OIL RIG” (Oxidation Is Loss, Reduction Is Gain) refers to electrons, not protons or oxygen alone.

Given Data / Assumptions:

• We are defining oxidation and reduction strictly by electron transfer.
• Protons (H+) may accompany electrons in some reactions but are not the defining criterion.
• Context includes biochemical carriers such as NAD+/NADH and FAD/FADH2.

Concept / Approach:
Oxidation is loss of electrons from a molecule, atom, or ion; reduction is gain of electrons. In biological systems, oxidations often involve dehydrogenation (loss of H as H− equivalent), while reductions involve hydrogenation (gain of electrons often with protons). Confusion arises when focusing on oxygen or protons; the universal definition centers on electrons.

Step-by-Step Solution:

Verification / Alternative check:
Track glucose oxidation to CO2: carbon atoms lose electrons, while O2 is reduced to H2O by gaining electrons, consistent with the definitions.

Why Other Options Are Wrong:

• Gain of electron: defines reduction, not oxidation.
• Loss/gain of protons: may accompany redox but is not the defining feature.

Common Pitfalls:
Assuming “oxidation” always involves oxygen; many biological oxidations do not directly add oxygen but still involve electron loss.

Final Answer:
loss of electron