Hydrogen Ion Concentration and pH Relationship

The pH of a solution is a measure of its acidity or alkalinity, and it is directly related to the concentration of hydrogen ions ($[H^+]$). The relationship is defined by the formula:

$ \text{pH} = -\log_{10}[H^+] $

This means that a lower pH value indicates a higher concentration of hydrogen ions, signifying a more acidic solution. Conversely, a higher pH value indicates a lower concentration of hydrogen ions (and a higher concentration of hydroxide ions), signifying a more alkaline or basic solution.

Identifying the Solution with Highest Hydrogen Ion Concentration

The question asks for the solution with the highest concentration of hydrogen ions. Based on the inverse relationship between pH and $[H^+]$, we need to find the option with the lowest pH value.

The given pH values are:

• pH = 10
• pH = 8
• pH = 4
• pH = 5

Comparing these values, pH = 4 is the lowest.

Conclusion

Since the solution with pH = 4 has the lowest pH value among the options, it possesses the highest concentration of hydrogen ions.