Pure water has a pH level of 7, which means it is neutral on the pH scale. If you want to increase the pH of water, you must add an alkaline substance to it. The pH scale ranges from 0 to 14, with anything above 7 being alkaline, and anything below 7 being acidic.
Isotonic solution
This is a solution in which there is no net movement of water into our out of the cell when a cell is placed in this solution. The solution is also dilute.
Well it’s pretty easy 7 - 15 is 8
