Which of the following are oxidation reactions? I. Rusting of iron II. Burning of fuel III. Rancidity of oils and fats IV. Browning of fruits. Select the correct answer using the code given below.

All four processes involve oxidation. (I) Rusting of iron: Fe is oxidised to Fe₂O₃·xH₂O by atmospheric oxygen and moisture. (II) Burning of fuel: hydrocarbons combine with O₂ to give CO₂ and H₂O — a combustion (oxidation) reaction. (III) Rancidity of oils and fats: unsaturated fats undergo oxidative degradation by atmospheric oxygen, producing foul-smelling aldehydes and ketones. (IV) Browning of fruits: cut fruits like apples turn brown due to enzymatic oxidation of phenolic compounds by atmospheric oxygen (catalysed by polyphenol oxidase). All four are oxidation reactions.