Electrons do not usually flow through the electron-transport chain to o2, unless adp is simultaneously phosphorylated to

ATP

Explanation:

The main purpose for cellular respiration, is to finally obtain ATP (Adenosine Triphosphate), this process occurres through the electron transport chain: this is the final step of the aerobic respiration, and takes place when energy from NADH and FADH₂ (both products from Krebs Cycle) is transferred to ATP  

This process occurres within the inner membrane of the mitochondria: while protons (H⁺) pass through the ATP synthase (this protein acts as a “tunnel” where H⁺ go through), which uses the difference of protons (H⁺) concentration between the matrix (between 2 mitochondrial membranes) and the inner matrix of mitochondria.  

The ATP synthase also acts as an enzyme, creating ATP using ADP + Pi (inorganic phosphorus)

The electrons used to help with this process, finally attach to O₂ (oxygen) to form H₂O

 The correct answer is :  ATP

Explanation:  The phosphorylation reaction is a type of metabolic reaction that results in the formation of (ATP) or (GTP) by the direct transfer and donation of a phosphoryl (PO3) group to (ADP) or (GDP) from a phosphorylated reactive intermediate. The breath is an ATP generating process in which an inorganic compound serves as the ultimate e-acceptor. O2 is delivered by blood flow.