Answer : The correct options is, (A) The acidity of a solution.
Explanation :
pH meter : It is a type of instrument which measures the activity of hydrogen ion in water based solution.
Or, pH measure the acidity or alkalinity of the solution.
Or we can say that, it will provide the most direct measure of pH by measuring the hydrogen ion concentration of a solution.
The pH range is, 1 to 14.
When the value of pH is less then 7 then the solution will be acidic.
When the value of pH is more then 7 then the solution will be basic.
When the value of pH is equal to 7 then the solution will be neutral.
Hence, the correct options is, (A) The acidity of a solution.