Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R). 

Assertion (A) : Most of ATP production by respiration is by oxidative phosphorylation.

Reason (R) : In respiration, it is the energy of oxidation reduction that is utilised for ATP production.

In light of the above statements, choose the correct answer from the options given below. 

Both (A) and (R) are true and (R) is the correct explanation of (A)

Assertion is true. Oxidative phosphorylation is a process that occurs during cellular respiration and is responsible for the majority of ATP synthesis in eukaryotic cells. It takes place in the inner mitochondrial membrane (or the plasma membrane in prokaryotes) and involves the coupling of electron transport with ATP synthesis. During oxidative phosphorylation, the flow of electrons through the electron transport chain (ETC) leads to the pumping of protons (H⁺) across the membrane, creating an electrochemical gradient. The energy stored in this gradient is then used to drive the synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate (Pi) through the enzyme ATP synthase.

Reason is also correct. In cellular respiration, the catabolic breakdown of respiratory substrates (such as glucose, fatty acids, and amino acids) involves oxidation-reduction (redox) reactions. During these reactions, electrons are transferred from one molecule to another, and this transfer of electrons is coupled with proton (H⁺) transfer. Oxidation is the loss of electrons, and reduction is the gain of electrons. The energy released during these redox reactions is harnessed to create an electrochemical gradient of protons (H⁺), which, in turn, drives the synthesis of ATP during oxidative phosphorylation.