An acidic soil is characterized by a pH level that is less than 7. In this context, the pH range of 1-6 directly indicates acidity, where lower values suggest a higher concentration of hydrogen ions in the soil. Soils with a pH of 6 are mildly acidic, and as you move toward 1, the acidity increases significantly.
In contrast, a pH of 7 is neutral, meaning that the soil is neither acidic nor alkaline. A range of 8-14 signifies alkaline conditions, with increasing alkalinity as the pH increases. The range of 4-8 encompasses both acid and neutral soils, but since it includes numbers above 7, it cannot solely represent acidic soils. Thus, the pH range 1-6 distinctly labels the soil as acidic, making it the correct answer for indicating acidic soil.