Answer:
C. Hydrogen Ions.
Explanation:
The pH level of soils is measured based upon the acidity or basicity level in the soil. The pH scale usually measures between 0-14. 7 is the neutral pH level of soil and a pH level below 7 is considered acidic and above 7 is alkaline.
So, soil with a high amount of hydrogen ions (H+) will be considered acidic. As the amount of hydrogen ions increases in the soil, the pH level of the soil decreases, making it acidic.
Therefore, option C is correct.
