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In the given options, the physical phenomenon is the oxidation of an iron nail (Oxidar un clavo de hierro).
1. Quemar kerosene (Burning kerosene): This is a chemical change involving the combustion of a fuel to produce heat, light, and other byproducts. It is a chemical phenomenon, not a physical one.
2. Oxidar un clavo de hierro (Oxidizing an iron nail): Oxidation is a chemical process where a substance loses electrons. In this case, the iron nail reacts with oxygen in the air, forming rust. This is a chemical phenomenon.
3. Fermentar un poco de chicha (Fermenting a bit of chicha): Fermentation is a biochemical process where sugars are converted into alcohol or acids by microorganisms like yeast or bacteria. This is a biological phenomenon.
4. Neutralizar la acidez estomacal (Neutralizing stomach acidity): Neutralization is a chemical reaction where an acid and a base react to form water and a salt, reducing the acidity. This is also a chemical phenomenon.
Therefore, the physical phenomenon in the given options is the oxidation of an iron nail.
