Final answer:
Lemon juice, with a pH of 3, prevents newly peeled potatoes from browning because its acidity inhibits the enzyme responsible for browning.
Step-by-step explanation:
When lemon juice, which has a pH of 3, is applied to newly peeled potatoes, it prevents them from browning due to its acidic nature. Browning of potatoes occurs when an enzyme called polyphenol oxidase reacts with oxygen in the air, resulting in the formation of brown pigments called melanins.
However, acidic conditions, like the one created by lemon juice, inhibit the activity of polyphenol oxidase and prevent the browning process.