What do you mean by elementary and their classification

The Classification of elementary students and the basis of their state of mind determines how they are and how they react to specific things.  

Explanation:

The classification of that specific person depends on their qualifications

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.