Question

The strength of an acid solution or a basic solution can be determined by knowing the hydrogen ion concentration in them, using a pH scale,
(i)- Neutral solution has pH 7.
(ii)- Acidic solution has pH less than 7.
(iii)- Basic solution has pH more than 7.
The pH of a solution is inversely proportional to hydrogen (${{H}^{+}}$) ion concentration in it.
Five students Ankit, Nitin, Deepika, Gunjan, and Pooja were given test tubes having solutions with pH 1.2, 13.5, 10.0, 7.4, and 2.2 respectively. The correct order of decreasing order of decreasing $O{{H}^{-}}$ ions concentration in these solutions is:
(a)- Ankit > Pooja > Gunjan > Deepika > Nitin
(b)- Nitin > Gunjan > Ankit > Pooja > Deepika
(c)- Deepika > Gunjan > Pooja > Nitin > Ankit
(d)- Nitin > Deepika > Gunjan > Pooja > Ankit

Answer 1

As stated in the question, pH is inversely proportional to the number of hydrogen ions in the solution. So lesser the hydrogen ions in the solution more will be the hydroxyl ions and the higher will be the pH of the solution. The more the hydrogen ions in the solution, the lesser will be the hydroxyl ions and the lower will be the pH.

Complete answer:
As stated in the question, pH is inversely proportional to the number of hydrogen ions in the solution. So lesser the hydrogen ions in the solution more will be the hydroxyl ions and the higher will be the pH of the solution. The more the hydrogen ions in the solution, the lesser will be the hydroxyl ions and the lower will be the pH.
So we can say that the pH of the solution is directly proportional to the number of hydroxyl ions in the solution.
Ankit has a test tube having a solution of pH 1.2, so the solution has very low pH, having a high amount of ${{H}^{+}}$ ions and a very low amount of $O{{H}^{-}}$ ions.
Nitin has a test tube having a solution of pH 13.5, so the solution has very high pH, having a low amount of ${{H}^{+}}$ ions and a very high amount of $O{{H}^{-}}$ ions.
Deepika has a test tube having a solution of pH 10.0, so the solution has high pH, having a low amount of ${{H}^{+}}$ ions and a high amount of $O{{H}^{-}}$ ions.
Gunjan has a test tube having a solution of pH 7.4, so the solution has almost neutral pH, having the almost same amount of ${{H}^{+}}$ ions and $O{{H}^{-}}$ ions.
Pooja has a test tube having a solution of pH 1.2, so the solution has very low pH, having a high amount of ${{H}^{+}}$ ions and a very low amount of $O{{H}^{-}}$ ions.
So the decreasing order of solutions having $O{{H}^{-}}$ ions in the test will be:
(d)- Nitin > Deepika > Gunjan > Pooja > Ankit

Therefore, the correct answer is an option (d).

Note:
If the solution has a pH between 0-3, then the solution is a strong acid. If the solution has a pH between 3-6.9, then the solution is a weak acid. If the solution has a pH between 7.1-10, then the solution is a weak base. If the solution has a pH between 10-14, then the solution is a strong base.