Final answer:
The reaction H₂O → O₂ suggests the decomposition of water, where hydrogen atoms are separated from oxygen leading to the release of oxygen gas. This separation represents a loss of hydrogen atoms from water, and in terms of redox reaction, it's an oxidation process because hydrogen atoms are losing electrons to oxygen. The correct option is 4.
Step-by-step explanation:
The reaction H₂O → O₂ appears to be a decomposition of water, which is not the usual representation as decomposition would produce both hydrogen gas and oxygen gas.
If considering the breakdown of water into oxygen, it would involve a loss of hydrogen atoms from the water molecule.
In terms of redox reactions, considering water (H₂O) transforming into oxygen gas (O₂), the reaction is a loss of electrons for the hydrogen atoms because they are separated from the oxygen atoms, leaving the hydrogen atoms oxidized.
Oxidation involves the loss of electrons, gain of oxygen, or loss of hydrogen atoms in a molecular compound.
In this scenario, it's the hydrogen atoms of the water molecule which undergo oxidation as they lose electrons to oxygen, resulting in their separation from oxygen atoms, which is an indication of a redox reaction. The correct option is 4.