Answer: <u>Option 4; Oxygen gains electrons and hydrogen to form water.
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Respiration is a process where glucose is used and energy is released stored in this molecule. Oxygen is used during respiration as well and it gains the electrons and hydrogen to form water. And, gain of electrons is an oxidation reaction. So answer is option 4.
Since, oxygen is consumed during respiration, option 1 is incorrect.
Loss of electrons is reduction, so option 2 is also incorrect.
Glucose is used in respiration, thus option 3 is incorrect.
