pH less than 7 indicates a solution that is:

The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is defined by the formula: $$pH = -\log[H^+]$$ On the standard pH scale (at $25^\circ\text{C}$): 1. **Neutral Solutions:** Have a $pH = 7$. Pure water is a classic example where the concentration of hydrogen ions $[H^+]$ equals the concentration of hydroxide ions $[OH^-]$. 2. **Acidic Solutions:** Have a $pH < 7$. These solutions have a higher concentration of hydrogen ions $[H^+]$ than pure water. 3. **Basic (Alkaline) Solutions:** Have a $pH > 7$. These solutions have a lower concentration of hydrogen ions (and a higher concentration of $[OH^-]$) than pure water. Since the question asks about a solution with a pH less than 7, it is classified as **Acidic**.