The pH of a lake decreases due to acid rain. Adding lime raises the pH. What type of process is this?

Correct answer: Neutralisation

Acid rain introduces acidic substances into the lake and lowers its pH. Lime is a basic material, commonly represented by calcium oxide or calcium hydroxide in this context. It reacts with acidic substances and reduces their acidity, thereby raising the pH toward a less acidic value. This acid–base reaction is neutralisation, not evaporation, condensation, or decomposition. Hence option A is correct.