Final answer:
Acidic soil is caused by hydrogen ions (H) which lower the pH level of the soil. This can occur naturally or through human activities.
Step-by-step explanation:
Acidic soil is caused by hydrogen ions (H). When hydrogen ions are released into the soil, they lower the pH level, making the soil more acidic. This can happen due to natural processes such as the decomposition of organic matter or through human activities like the use of fertilizers that release hydrogen ions.
Learn more about Causes of acidic soil