Which value indicates a more acidic solution?

A more acidic solution is reflected by a lower pH value on the pH scale, which ranges from 0 to 14. The scale is logarithmic, meaning each whole number change represents a tenfold change in acidity or alkalinity. A pH value of 7 is considered neutral, meaning it is neither acidic nor basic.

Values below 7 indicate increasing acidity, with 0 being the most acidic. Therefore, a pH of 4 signifies a solution that is acidic, as it falls significantly below the neutral point of 7. In contrast, a pH of 8 indicates a basic (alkaline) solution, and a pH of 10 is even further towards the basic side. Hence, the value of 4 is indeed the most indicative of acidity in this context, making it the correct choice.