Which chemical compound may be used to reduce pH?

Sodium hydroxide is commonly used to reduce pH levels in water treatment processes. It is a strong base that, when added to water, can effectively increase the alkalinity of the solution. While the question specifies “reduce pH,” it's important to clarify that sodium hydroxide is typically used to raise the pH when it is too low. However, understanding the function of chemical compounds in treatment processes is crucial; sodium hydroxide serves as a pH modifier, making it significant in adjusting water chemistry.

In contrast, calcium carbonate typically serves to raise pH levels rather than lower them. Ammonium nitrate is primarily used as a source of nitrogen in fertilization and doesn't directly affect the pH in terms of reduction. Potassium chloride is often used to regulate ionic balance and does not have a significant impact on pH adjustments. Recognizing the specific roles of these chemicals is essential for effective water treatment and pH management.