Final answer:
On-the-scalp lighteners have a pH that is alkaline, with a pH value greater than 7. This is in line with the pH scale, where values above 7 indicate basic or alkaline solutions.
Step-by-step explanation:
The pH scale is a measurement that indicates the acidity or basicity of a solution. When it comes to on-the-scalp lighteners, their pH is generally alkaline, meaning the pH is above 7. The pH scale typically ranges from 0 to 14. Therefore, the correct answer to the question is C) Alkaline (pH > 7).
To elaborate, the pH of a solution is the negative logarithm of the hydrogen ion concentration, shown by the equation pH = -log[H3O+]. A pH level below 7 signifies an acidic solution, a pH level of 7 indicates a neutral solution, and a pH level above 7 indicates that the solution is basic or alkaline. It's important to note that the pH scale can extend beyond 0 and 14 in very strong acids or bases, although this is not common in everyday solutions.