For concentrated HClO4, it is about -15 +/- 2.

The pH of a solution is a measure of the concentration of hydrogen ions in the solution. A solution with a high number of hydrogen ions is acidic and has a low pH value. A solution with a high number of hydroxide ions is basic and has a high pH value. The pH scale ranges from 0 to 14, with a pH of 7 being neutral.

The pH of a solution is a measure of the concentration of hydrogen ions in the solution. A solution with a high number of hydrogen ions is acidic and has a low pH value. A solution with a high number of hydroxide ions is basic and has a high pH value.

As the concentration of hydrogen ions in a solution increase, the more acidic the solution becomes. As the level of hydroxide ions increases the more basic, or alkaline, the solution becomes. Thus, as the hydrogen ion concentration increases hydroxide ion concentration falls, and vice versa. …

Anything below 7.0 is acidic, and anything above 7.0 is alkaline, or basic. pH scale, ranging from 0 (very acidic) to 14 (very basic/alkaline) and listing the pH values of common substances.

pH = -log (M) = -log(2.1M) = -0.32, which is clearly a negative number.

0.23

So the pH of the solution is going to be -0.3.

1.60

0.602

1.83

pH 2.0