AMPP Cathodic Protection Technician (CP2) Practice Exam 2025 - Free CP2 Practice Questions and Study Guide

Ammonium sulfate is commonly used as a fertilizer and is known to decrease soil pH when applied. This occurs because ammonium ions (NH4+) in the ammonium sulfate are transformed into ammonia (NH3) through microbial activity in the soil. During this process, hydrogen ions (H+) are released, which lowers the pH and makes the soil more acidic. This increase in hydrogen ions is what causes the reduction in soil pH, making ammonium sulfate an effective amendment for acidifying soil.

The other choices, while they may have some effects on soil properties, do not exhibit the same acidifying behavior as ammonium sulfate. For example, calcium sulfate and magnesium sulfate do not have a significant acidifying effect, and carbon sulfate is not a common term or recognized compound associated with wielding such influence on soil pH. Thus, the distinct behavior of ammonium sulfate in lowering soil pH is what makes it the correct answer in this context.